Worm (or piece) should be around same as frog's SVL. Can cut worms from pointy end and they should heal. If frog is not associating worm with food, feed 1 cricket or roach. Then take worm piece in tongs and approaching from face side, lightly rub it's mouth with it. Maybe that will elicit a hit. Once it eats one; the rest should be easy. Good luck !