search firebase document for a specific field in flutter dart and store it

Question

im trying to restore a document that its field "email" equal to certain value my code didnt get me anything dont know what is the problem

 void EditDisplayedName(String email, String name) async {
  CollectionReference s = FirebaseFirestore.instance
      .collection("Users")
      .doc("list_instructors")
      .collection("Instructor")
    ..where("Email", isEqualTo: email);

  s.doc(email).update({'Full Name': name});
} //end method