How can I access specific data in Firebase?

Question

I want to delete the messages of every user before 30 days. When the user enters the application, their own messages are deleted. But I can't access every user's messages. I couldn't find what to write for the query.

This my message db:

This my Code to delete messages when the user opens an account :

   mAuth = FirebaseAuth.getInstance();
        currentUserID = mAuth.getCurrentUser().getUid();
        ChatsRef = FirebaseDatabase.getInstance().getReference().child("message").child(currentUserID);
     

 long cutoff = new Date().getTime() - TimeUnit.MILLISECONDS.convert(30, TimeUnit.DAYS);
        Query oldItems = ChatsRef.orderByChild("timestamp").endAt(cutoff);
        oldItems.addListenerForSingleValueEvent(new ValueEventListener() {
            @Override
            public void onDataChange(DataSnapshot snapshot) {
                for (DataSnapshot itemSnapshot: snapshot.getChildren()) {
                    itemSnapshot.getRef().removeValue();
                }
            }

            @Override
            public void onCancelled(DatabaseError databaseError) {
                throw databaseError.toException();
            }
        });

How can I access the timestamp of each user?

Update My users db: