React native – How to position a button at the bottom

I have a react native component and I am trying to put the touchable opacity button at the bottom of the map(but over the map with zIndex). But for some reason I can’t achieve this. I have provided part of the code as following. also I don’t understand why the button is appearing at the top before the map? i have also attached a photo of how the app looks like for different codes.

 return (
    <SafeAreaView style={{paddingHorizontal:4,paddingTop:12}}>
      <Text style={{fontSize:16,fontWeight:"bold",marginLeft:6}}>Please Type your address in the box below</Text>
      <Text>Your address is only used to filter neaerby listings of items.</Text>
      <TextInput 
      value={address}
      onChangeText={changeAddress}
      placeholder='Set Your address here'
      style={styles.Pasinput}
      />
      {
        address && !showmap && <ShowFlatlistAddress navigation={navigation} stAddrs={setAddress} addresses={addressToDisplay} flag={flagUrl} phoneC={phoneCode} stshowmap={setshowmap}/>
      }
      {
        showmap && 
        <View style={{flex:1}}>
            <MapView
          provider={PROVIDER_GOOGLE}
          initialRegion={{
            latitude: 37.78825,
            longitude: -122.4324,
            latitudeDelta: 0.0922,
            longitudeDelta: 0.0421,
          }}
          zoomEnabled={true}
          zoomControlEnabled={true}
          style={{flex:1,height:height*1,width:width*1,...StyleSheet.absoluteFillObject}}
          >
          <Marker
            draggable
            coordinate={{
              latitude: 37.78825,
              longitude: -122.4324,
            }}
            onDragEnd={
              (e) => alert(JSON.stringify(e.nativeEvent.coordinate))
            }
            title={'Test Marker'}
            description={'This is a description of the marker'}
          />
        </MapView>
        <TouchableOpacity
        style={{position:"absolute",backgroundColor:"orange",zIndex:3,padding:12}}
        onPress={()=>{
          navigation.navigate("Verfication",{addressSet:address,flagC:flagUrl,phoneCodes:phoneCode})
        }}
        >
          <Text style={{fontSize:24,textAlign:"center"}}>Confirm Address</Text>
        </TouchableOpacity>
        </View>
      }
    </SafeAreaView>
  )