I'm going to bet that they did not disconnect the airbag. Getting the bloody thing off the column is such a pain. I would be more inclined to say they disconnected the plugs under the carpeting, or removed the module under the seat completely, and then probably removed the light from the instrument cluster.

First thing to do: Turn your key on (car not started) and see if the SRS light lights. It's right next to the odometer reset. If not, I would go digging for disconnected stuff.

Remove the left side dash center console panel. If you reach down into the carpet, you'll likely find the yellow plug that goes to the ECU which is under the seat. If you don't find both halves, good chance they removed the ECU. If you do find both halves, disconnected, clean them thoroughly. Bad contacts in that plug cause lots of faults. Plug it back in.

If the bulb in the cluster was not working, pull the cluster and put one in there. It's part of the system. No bulb, no SRS.

Once you have a working bulb, you can move on to any diagnostics, provided you have an ECU and it's connected, and the bulb is working. Running diagnostics is a different story. I have a document on that which I can send you if you message.

If the airbag has been disconnected, which is a possibility, you will need to remove the screws from the front side that go through the steering wheel. They are Torx, and are a real pain to get to and pull.

Whenever you are working on the SRS, it's not a bad idea to disconnect the battery.

DS

This is not a straight forward answer because it could be in multiple places. My guess is that he unplugged the air bag module itself on the steering wheel. If that is the case then it is a reasonably simple job. Obviously disconnect the battery before trying this. I suggest that you purchase or look at a Bently manual which displays a good drawing of the SRS (air bag) system.

Mark