A few months ago I was in the same situation. What I did:
Buy frozen shrimp or fresh tilapia from local supermarket( make sure there is nothing chemically added)
Thaw out shrimp or tilapia and cut in to but-sized pieces. Stuff a pellet inside the shrimp or tilapia. If you drop it in and he doesn’t eat it, do it again but put it on some fishing line or some string and jerk it through the tank( make sure the bass can pull it off the string). The bass will for sure eat it if you make it look like a fish in the water. Do this for a week or so and do everything you do infront of the tank so the bass can see you and repeat the motions. Every few days, trick him by dropping a pellet in first. Make sure the pellet is the first thing you drop in when you go to try to trick him. Good luck!