Generalice los queries en Confirm.js, cree el chat de la cita, borro la cita si me dicen que no, notifico al usuario. Anadi un field 'new' a appointments para saber cuales que appointments hay que halar en el screen de citas. Se pone en false si se acepta.

screens/main/Cita.js

 import Constants from 'expo-constants';
 import * as Notifications from 'expo-notifications';
 
-Notifications.setNotificationHandler({
-  handleNotification: async () => ({
-    shouldShowAlert: true,
-    shouldPlaySound: true,
-    shouldSetBadge: false,
-  }),
-});
 
 
 export function Cita({navigation}) {
-  const [threads, setThreads] = useState([]);  
-  const [loading, setLoading] = useState(true);
-  const [appointments, setAppointments] = useState([]); 
-
-  const [expoPushToken, setExpoPushToken] = useState('');
-  const [notification, setNotification] = useState(false);
-  const notificationListener = useRef();
-  const responseListener = useRef();
-
-  useEffect(() => {
-    registerForPushNotificationsAsync().then(token => setExpoPushToken(token));
-    notificationListener.current = Notifications.addNotificationReceivedListener(notification => {
-      setNotification(notification);
-    });
-
-    responseListener.current = Notifications.addNotificationResponseReceivedListener(response => {
-      console.log(response);
-      navigation.navigate('Confirm');
-    });
-
-    const fire = firebase.firestore()
-    .collection('THREADS')
-    .where("members", "array-contains", firebase.auth().currentUser.uid)
-    .onSnapshot(querySnapshot => {
-      const threads = querySnapshot.docs.map(documentSnapshot => {
-        return{
-          _id:documentSnapshot.id,
-          name:'',
-          ...documentSnapshot.data()
-        };
-      });
-
-      setThreads(threads);
-      console.log(threads);
-
-      if(loading){
-        setLoading(false);
-      }
-    });
-
-    const cita = firebase.firestore().collection('APPOINTMENTS').where('Day', '==', 8).onSnapshot(snapShot => {
-      const appointments = snapShot.docs.map(docSnap => {
-        return{
-          _id:docSnap.id,
-          Day:'',
-          Month:'',
-          Time:'',
-          i_id:'',
-          uid1:'',
-          ...docSnap.data()
-        };
-      });
-      setAppointments(appointments);
-      console.log(appointments);
-    });
-      
-    return () => {
-      Notifications.removeNotificationSubscription(notificationListener.current);
-      Notifications.removeNotificationSubscription(responseListener.current);
-      fire();
-      cita();
-    }
-  }, []);
-  
-  if (loading) {
-    return <Loading />;
-  }
+   
 
   
-  function handleButtonPress() {
-      firebase.firestore()
-        .collection('THREADS')
-        .add({
-          name: 'PedroFecha',
-          members: [
-            firebase.auth().currentUser.uid,
-            '02yOZHxFcGUX4MNwjeEbAlCShdu1'
-          ]
-        })
-  }
 
   const dimensions = Dimensions.get('window');
   const screenWidth = dimensions.width;
   
   return (
       <ImageBackground style={styles.stdcontainer} source={require('../../assets/yellow-white.jpg')}>
-        <FlatList style={{
-             flex: 1,
-             width: screenWidth,
-         }}
-          data={threads}
-          keyExtractor = {item => item._id}
-          ItemSeparatorComponent={() => <Divider />}
-          renderItem = {({item}) => (
-          <TouchableOpacity
-            onPress={() => navigation.navigate('Room', {thread: item})}
-          >
-            <List.Item
-              title={item.name}
-              titleNumberOfLines={1}
-              titleStyle={styles.listTitle}
-              descriptionStyle={styles.listDescription}
-              descriptionNumberOfLines={1}
-            />
-          </TouchableOpacity>
-        )}
-        />
-        <FlatList style={{
-             flex: 1,
-             width: screenWidth,
-         }}
-          data={appointments}
-          keyExtractor = {item => item._id}
-          ItemSeparatorComponent={() => <Divider />}
-          renderItem = {({item}) => (
-          <TouchableOpacity
-          onPress={async () => {
-            await sendPushNotification(expoPushToken); //item.push_token
-          }}
-          >
-            <List.Item
-              title={item.Month}
-              titleNumberOfLines={1}
-              titleStyle={styles.listTitle}
-              descriptionStyle={styles.listDescription}
-              descriptionNumberOfLines={1}
-            />
-            <List.Item
-              title={item.Day}
-              titleNumberOfLines={1}
-              titleStyle={styles.listTitle}
-              descriptionStyle={styles.listDescription}
-              descriptionNumberOfLines={1}
-            />
-            <List.Item
-              title={item.Time}
-              titleNumberOfLines={1}
-              titleStyle={styles.listTitle}
-              descriptionStyle={styles.listDescription}
-              descriptionNumberOfLines={1}
-            />
-          </TouchableOpacity>
-        )}
-        />
       <Button
         title ='Ver mapa'
         onPress= {() => navigation.navigate('Map')}
         </ImageBackground>
     );
   }
-// Can use this function below, OR use Expo's Push Notification Tool-> https://expo.dev/notifications
-async function sendPushNotification(expoPushToken) {
-  const message = {
-    to: expoPushToken,
-    sound: 'default',
-    title: 'Freehand',
-    body: 'Le solicitan una cita',
-    data: { someData: 'goes here' },
-  };
-
-  await fetch('https://exp.host/--/api/v2/push/send', {
-    method: 'POST',
-    headers: {
-      Accept: 'application/json',
-      'Accept-encoding': 'gzip, deflate',
-      'Content-Type': 'application/json',
-    },
-    body: JSON.stringify(message),
-  });
-}
-
-async function registerForPushNotificationsAsync() {
-  let token;
-  if (Constants.isDevice) {
-    const { status: existingStatus } = await Notifications.getPermissionsAsync();
-    let finalStatus = existingStatus;
-    if (existingStatus !== 'granted') {
-      const { status } = await Notifications.requestPermissionsAsync();
-      finalStatus = status;
-    }
-    if (finalStatus !== 'granted') {
-      alert('Failed to get push token for push notification!');
-      return;
-    }
-    token = (await Notifications.getExpoPushTokenAsync()).data;
-    console.log(token);
-  } else {
-    alert('Must use physical device for Push Notifications');
-  }
-
-  if (Platform.OS === 'android') {
-    Notifications.setNotificationChannelAsync('default', {
-      name: 'default',
-      importance: Notifications.AndroidImportance.MAX,
-      vibrationPattern: [0, 250, 250, 250],
-      lightColor: '#FF231F7C',
-    });
-  }
-
-  firebase.firestore().collection('Interprete').doc(firebase.auth().currentUser.uid).update({'push_token': token})
-  firebase.firestore().collection('Users').doc(firebase.auth().currentUser.uid).update({'push_token': token})
 
-  return token;
-}
 
 const mapStateToProps = (store) => ({
   currentUser: store.userState.currentUser

screens/main/Confirm.js

       }
     });
 
-    const cita = firebase.firestore().collection('APPOINTMENTS').where('Day', '==', 8).onSnapshot(snapShot => {
+    const cita = firebase.firestore().collection('APPOINTMENTS').where("new", "==", 'true').onSnapshot(snapShot => {
       const appointments = snapShot.docs.map(docSnap => {
         return{
           _id:docSnap.id,
+          participantes: '',
+          new: '',
           Day:'',
           Month:'',
           Time:'',
-          i_id:'',
-          uid1:'',
+          i_token:'',
+          u_token:'',
           ...docSnap.data()
         };
       });
       setAppointments(appointments);
-      console.log(appointments);
+      console.log("appointment", appointments);
+      //console.log(appointments.Day);
     });
       
     return () => {
     return <Loading />;
   }
 
-  
-  function crearChat() {
-      firebase.firestore()
-        .collection('THREADS')
-        .add({
-          name: 'CHAT',
-          members: [
-            firebase.auth().currentUser.uid,
-            '02yOZHxFcGUX4MNwjeEbAlCShdu1'
-          ]
-        })
+
+  function crearChat(cliente, citaID) {
+    firebase.firestore()
+      .collection('THREADS')
+      .add({
+        name: 'CHAT',
+        members: [
+          firebase.auth().currentUser.uid,
+          cliente, 
+        ],
+        cita: citaID,
+      })
+}
+
+
+  function citaOld(docID) {
+    firebase.firestore()
+      .collection('APPOINTMENTS')
+      .doc(docID)
+      .update({
+        new: 'false',
+      })
+  }
+
+  function deleteAppointment(docID) {
+    firebase.firestore()
+      .collection('APPOINTMENTS')
+      .doc(docID)
+      .delete()
   }
 
   const dimensions = Dimensions.get('window');
              flex: 1,
              width: screenWidth,
          }}
-          data={threads}
-          keyExtractor = {item => item._id}
-          ItemSeparatorComponent={() => <Divider />}
-          renderItem = {({item}) => (
-          <TouchableOpacity
-            onPress={() => navigation.navigate('Room', {thread: item})}
-          >
-            <List.Item
-              title={item.name}
-              titleNumberOfLines={1}
-              titleStyle={styles.listTitle}
-              descriptionStyle={styles.listDescription}
-              descriptionNumberOfLines={1}
-            />
-          </TouchableOpacity>
-        )}
-        />
-        <FlatList style={{
-             flex: 1,
-             width: screenWidth,
-         }}
           data={appointments}
           keyExtractor = {item => item._id}
           ItemSeparatorComponent={() => <Divider />}
         title ='Ver mapa'
         onPress= {() => navigation.navigate('Map')}
       />
-      <Button
-        title="No disponible"
-        onPress={async () => {
-          await sendPushNotification(expoPushToken); //item.push_token
-          //Borrar Appointment de fb
-          navigation.navigate('Home');
-        }}
-      /> 
-      <Button
-        title ='Si'
-        onPress= {() => {
-            crearChat();
-            navigation.navigate('Home');
-        }}
+      <FlatList style={{
+             flex: 1,
+             width: screenWidth,
+         }}
+          data={appointments}
+          keyExtractor = {item => item._id}
+          renderItem={({ item }) => {
+            if(item.new){
+            return (
+              <Button
+               title="No disponible"
+               onPress={async () => {
+               await sendPushNotification(item.u_token);
+               deleteAppointment(item._id);
+               navigation.navigate('Home');
+               }}
+             /> 
+            )
+          }}}
       />
+      <FlatList style={{
+             flex: 1,
+             width: screenWidth,
+         }}
+          data={appointments}
+          keyExtractor = {item => item._id}
+          renderItem={({ item }) => {
+            if(item.new){
+            return (
+              <Button
+              title ='Sí'
+              onPress={ async () => {
+                citaOld(item._id)
+                crearChat(item.participantes[0], item._id)
+                navigation.navigate('Home');
+                }
+              }
+            /> 
+            )
+          }}}
+            />
         </ImageBackground>
     );
   }

screens/main/Home_page.js

   const notificationListener = useRef();
   const responseListener = useRef();
 
-  //const [oneApp, setOneApp] = useState('')
-
 
   useEffect(() => {
     registerForPushNotificationsAsync().then(token => setExpoPushToken(token));
 
     responseListener.current = Notifications.addNotificationResponseReceivedListener(response => {
       console.log(response);
-      navigation.navigate('Confirm');
+      if (response.notification.request.content.body == 'Le solicitan una cita'){
+        navigation.navigate('Confirm');
+      } 
     });
 
     const fire = firebase.firestore()
       });
 
       setThreads(threads);
-      //console.log(threads);
 
       if(loading){
         setLoading(false);
       }
     });
 
-    const cita = firebase.firestore().collection('APPOINTMENTS').where("participantes", "array-contains", 'qj5xBCSRNoaRMik4UULmslSktLp1').onSnapshot(snapShot => {
+    const cita = firebase.firestore().collection('APPOINTMENTS').where("participantes", "array-contains", firebase.auth().currentUser.uid).onSnapshot(snapShot => {
       const appointments = snapShot.docs.map(docSnap => {
         return{
           _id:docSnap.id,
+          new:'',
           Day:'',
           Month:'',
           Time:'',
       });
       setAppointments(appointments);
       console.log("appointment", appointments);
-      //console.log(appointments.Day);
     });
 
-
-    const day = firebase.firestore().collection('APPOINTMENTS').where('Day', '==', 8).get().then((res) => {
-      console.log(`Day is ${res.docs[0].get('Day')}.`);
-      //const dia = return{`${res.doc[0].get('Day')}`};
-    });
-    //console.log("Day", dia);
       
     return () => {
       Notifications.removeNotificationSubscription(notificationListener.current);
   }
    
   
-
-  
-  function handleButtonPress() {
-      firebase.firestore()
-        .collection('THREADS')
-        .add({
-          name: 'PedroFecha',
-          members: [
-            firebase.auth().currentUser.uid,
-            '02yOZHxFcGUX4MNwjeEbAlCShdu1'
-          ]
-        })
-  }
-
   const dimensions = Dimensions.get('window');
   const screenWidth = dimensions.width;
 
         renderItem = {({item}) => (
         <TouchableOpacity
         onPress={async () => {
-          navigation.navigate('Cita')
+          navigation.navigate('Cita', {appointment_id: item._id})
         }}
         >
           <List.Item
       )}
           />
         <Button
-            title ='Send notification'
-            onPress={async () => {
-            await sendPushNotification(expoPushToken);
-            }}
-          /> 
-        <Button
           title ='Hacer Busqueda'
           onPress= {() => navigation.navigate('Search')}
         />
           keyExtractor = {item => item._id}
           ItemSeparatorComponent={() => <Divider />}
           renderItem={({ item }) => {
+            if(item.new){
             return (
               <Button
-              title ='Send notification'
+              title ='Pedir Cita'
               onPress={ async () => {
                 await sendPushNotification(item.i_token);
                 }
               }
             /> 
             )
-          }}
+          }}}
             />
 
 
           <Button
-            title ='Send notification'
-            onPress={async () => {
-            await sendPushNotification(expoPushToken);
-            }}
-          /> 
-          <Button
           title ='Availability'
           onPress= {() => navigation.navigate('Availability')}
         />
-        <Button
-          title ='Mapa'
-          onPress= {() => navigation.navigate('Map')}
-        />
           <Button
             title ='Logout'
             onPress= {() => firebase.auth().signOut()}

screens/main/StateTime.js

       i_id,
       uid, 
       ],
+      new: true,
       Month : month,
       Day: day,
       Time: _time_,
       i_id,
       uid, 
       ],
+      new: true,
       Month : month,
       Day: day,
       Time: _time_,