SignIn.js

...
import auth from '@react-native-firebase/auth';
...

 const __signIn = async () => {
    try {
      let response = await auth().signInWithEmailAndPassword(UserEmail, UserPassword)
      if (response) {
        console.log(response)
        Alert.alert('Successful Login','Welcome the React Native')
      }
    } catch (e) {
      console.error(e.message)
    }
  }
 
...
onPress={() => __signIn()}