try not to handle him right now until he starts eating on his own (just handle for spoon feeding). handling might be causing him some stress and stress can lead to not eating.

89 degrees is good for the warm side. what is the cool side temp? maybe that is too low? around 80 is good.

you might add some hides for him around the tank to help make him feel secure right now.

keep a dish of mealworms in the tank with him at all times so he can munch if he wants to. count the mealworms each day so you know if he ate any or not. if you offer crickets remove any that he doesn't eat within an hours time and don't leave them with him overnight until he starts eating regularly. at that point they can be left in for 24 hours.

does his abdomen seem bloated or distended at all? is it discolored or bruised looking? what type of substrate did the person who had him keep him on and what are you keeping him on now? (i'm looking for any potential signs that he could be impacted.)

also, how old is the gecko?