As I said the command RX does not work.
RX is not a command. RX is a variable which is assigned an ASCII code when serin2 is executed.

I see you changed IF THEN to SELECT CASE. SELECT CASE is for values and not ASCII characters like "A".

Did it stop working when you made these changes?
Did you make these changes because it did not work with IF THEN?
Is the servo working if not has the servo ever worked?