How to attach email to Angular10 FormGroup?

I can’t find a way to attach user email to FormGroup to send it to Firebase… I need some help.

This is part of my component:

export class ProductComponent implements OnInit {

  secondForm = new FormGroup({ valueToGet: new FormControl('') })

  single;

  email;

  ref: AngularFireStorageReference;
  task: AngularFireUploadTask;
  uploadProgress: Observable<number>;
  downloadURL: string;

  myArray: any[] = []

  edit: boolean = false

  form = new FormGroup({
        image: new FormControl(''),
        subject: new FormControl(''),
        comment: new FormControl(''),
        email: new FormControl('')
    })

  constructor(private firestore: AngularFirestore, public authService: AuthService, private afStorage: AngularFireStorage) { }

  ngOnInit() {
    this.firestore
  .collection("testCollection")
  .get()
  .subscribe((ss) => {
    ss.docs.forEach((doc) => {
      this.myArray.push(doc.data());
    });
  });
   this.docs = [];
        const collectionRef = this.db.collection('testCollection');
        const collectionInstance = collectionRef.valueChanges();
        collectionInstance.subscribe(ss => this.myArray = ss);
  }

  onSubmit() {
        this.firestore.collection('testCollection').add({
            image: this.form.value.image,
            subject: this.form.value.subject,
            comment: this.form.value.comment,
            email: this.authService.getEmail(this.email)
        })
        .then(res => {
            console.log(res);
            this.form.reset();
        })
        .catch(e => {
            console.log(e);
        })
    }

And this is my auth.service:

export class AuthService {


  user: AngularFireAuth['user'];

  constructor(private firebaseAuth: AngularFireAuth) {
    this.user = firebaseAuth.authState;
  }

  async showErrorAlert() {
          Swal.fire('Invalid Email or Password!')
        }

  signup(email: string, password: string) {
    this.firebaseAuth
      .createUserWithEmailAndPassword(email, password)
      .then(value => {
        console.log('Success!', value);
      })
      .catch(err => {
        console.log('Something went wrong:',err.message);
      });
  }

  login(email: string, password: string) {
    this.firebaseAuth
      .signInWithEmailAndPassword(email, password)
      .then(value => {
        console.log('Nice, it worked!');
      })
      .catch(err => {
        this.showErrorAlert();
        console.log('Something went wrong:',err.message);
      });
  }

  getEmail(email) {
    return this.email = email;
  }

Source: Angular Questions