Is he actually stuck in it? or is he stuck inside it?.. if he's stuck inside it.. leave it be. they are very good at wedging themselves inside things, trying to get him out will likely cause alot of damage to the fish. It may take time. but try putting in some safer hiding spots for him such as PVC tubes, or a piece of driftwood. You can also try baiting him out with food. When he comes out, get rid of it. If he's literally stuck, it's hard to do. I've carefully removed deco, and slathered a fish with stresscoat and was able to get it out w/ minimal damage. Pure aloe can also work. But it's very dangerous.