android – Firebase Add data to an existing item

I'm trying to add some djNames to one account, and it would be a one-to-many relationship. Here is what I have done so far:

enter the description of the image here

I want these two names to be assigned to "Aaron A". Here is what I have to insert the data into my database:

                                                final String djName = mDjName.getText (). toString ();
String singleID = mUniqueDjID.getText (). ToString ();
GoogleSignInAccount acct = GoogleSignIn.getLastSignedInAccount (RegisterDJActivity.this);
demoRef = rootRef.child ("djprofile");

if (acct! = null)
{
final String personName = acct.getDisplayName ();

demoRef.addListenerForSingleValueEvent (new ValueEventListener () {
@Override
public void onDataChange (@NoNull DataSnapshot dataSnapshot) {
if (dataSnapshot.hasChild (personName))
{
demoRef = rootRef.child (personName);
demoRef.push (). getParent (). child ("djName"). setValue (djName);
}
other
{
demoRef = rootRef.child ("djprofile");
demoRef.push (). child (personName) .child ("djName"). setValue (djName);
}

}

@Override
public void onCancelled (@NonNull DatabaseError databaseError) {

}
});

}