How to repeat Firestore query?

Hi I have problem with my code.

 final String range = "0123456789ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz";

 SecureRandom sr = new SecureRandom();

 randomString(8, range, sr);
 String code = randomString(8, AB, rnd);
 Log.d(TAG, code);

 Query codeQuery = collectionReference.whereEqualTo("ReferenceCode", code);
 codeQuery.get().addOnCompleteListener(new OnCompleteListener<QuerySnapshot>() {
     @Override
     public void onComplete(@NonNull Task<QuerySnapshot> task) {
         if (task.isSuccessful()) {
             for (DocumentSnapshot document : task.getResult()) {
                 if (document.exists()) {
                     String refCode = document.getString("ReferenceCode");
                     Log.d(TAG, "this code already exists");
                 } else {
                     Log.d(TAG, "this code does not exists");
                 }
             }
         } else {
             Log.d("TAG", "Error getting documents: ", task.getException());
         }
     }
 });

What I want to do is after (document.exists()) just repeat generating and checking existing the same code in database (so all above code).

How I can do this ?