He's hiding, you need to unhide him.
Surround him with 4 tiles that don't match his color.Technically you can reset everything using Ctrl+R (restarts pico8 or refreshes the page lol) technically there’s nothing to gain from resetting, since it’s always possible to shuffle the room/world back to its original state and the puzzles can’t be put into an unsolvable state. Also it’s just fun to see the big mess that is left over after plaything through the game.