get a feeding probe [or just use your fingers or a turkey baster] and nudge a little chopped or sliced ordinary people-food raw shrimp onto the disk. It will do the rest.
Are its tentacles out? You may have to encourage it a little with shrimp-juice [yep, you just squeeze hard].
Be sure you have it sitting on substrate, never on rocks. They're the one stony that will move if it doesn't like its position.