How to adjust gears and what could cause the malfunction light to go off and on. on 1998 Volkswagen Beetle TDI

My clutch was replaced and it will go into all gears except 5th. As for the malfuncton light, it was on prior to fixing the clutch and afterwards it didn't come on. But it came on suddenly when i put the AC on? I don't know if that was a coincidence or maybe it loosened a plug?

Asked by for the 1998 Volkswagen Beetle TDI