Automatic transmission not shifting

[Engir]

I meet someone with a 87 Cherokee XJ he was telling me the transmission will not change gears he has to shift it manually through the gears and that he thinks it is the TCM under the dash on the drivers side, I was thinking it is the TCC solenoid. What I want to ask is first how can I determine which it is and if it is the TCM is there a reset on it to try before replacing it?

Thanks