Refrigerator not cooling: told to unplug 24 hours
The odds of that working are very low. The guy probably said that because he was too busy to come so he just said that to give you something to do in the hope that you would call again later when he had more scheduling availability.

The most likely possibility is that it is the internal overload breaker. Usually it is easy to reset with a screw driver. Here is a picture of a typical one:



The hole has a little slot where you insert the screw driver and give it a half turn to reset it.

Of course, it could be a range of other problems, like a broken controller or a broken temperature sensor, too, but the reset is an easy thing to try.