Is there a cure for ringworm on the scalp?

OTC creams. Ringworm is actually a fungal infection (not a worm) of the skin. You can treat it with over the counter antifungals such as Clotrimazole cream (and there are many others). Clean the area, dry it and then apply the cream several times per day. If it persists longer than about 2 weeks, you might want to see a dermatologist for alternative applications.