Awe . I agree, if it doesn't retract back in soon I think he'll need a vet. A volvulus or the stomach sliding up through itself if there too long can lose circulation. A qualified vet can carefully slide it back through itself. Caution should be taken to not twist it. Keep him moist. It would be wise to not feed him for at least 24 hours of having the stomach put back in to allow the swelling to decrease. You can soak him though.