getting the radio code to work?

My Renault Megane has had some work done on the engine and now the radio/ tape doesn't work. The immobilizer for the car is working fine though.

I have the 4 digit code and managed to put in the last digit of the 4 digit code using the radio channel changer on the steering wheel, and when the last digit is flashing - I don't know what to do after or what to press. The radio vdu just says CODE again. None of the buttons appear to be functioning on the actual radio/ tape bit on the dash. Can you help?