How can you display text from Firestore?

I am trying to make an app with React Native, Firebase, and Expo that shows text that is loaded from the Firestore.

For example, I want the app to display "helloworld".

My Firebase backend looks like this:

But I don't know how to load the text from Firestore into the app and how to display it.

First add library 'react-native-firebase'

import firebase from 'react-native-firebase';

Then get the data from firestore using below function

getDataFromFirebase(){
firebase.firestore().collection('testcollections').doc(testdoc).get()
     .then((doc) => {
        if (doc.exists) {
          console.log("Document data: ", doc.data().testfield);
        }else{
          console.log("Document data is not empty: ");
        }
      })
    .catch(error => {
      console.log('firebase Error::'+error)
     })
}