Dandruff shampoo is supposed to be good for scalp ringworm. Petroleum jelly and nail polish supposedly works as well. These apparently suffocate the fungi and cause it to die.
I personally would rather stick to proven treatments-- either over-the-counter anti-fungal creams or prescription anti-fungal creams, sprays and tablets.
I once had ringworm that I think I got from the gym or the pool. My doctor gave me a topical spray for it as well as tablet anti-fungal medication. The infection cleared up in a week.