Peekawho is correct! Only surgery can correct a cherry eye. They are usually not painful, but may be itchy, or irritating, because the third eye lid can become dried out.
Moistening several times per day may be necessary with an eye ointment or drop that contains an antibiotic and/or steroid. You will have to get this from your vet.
I don't think there is anything that will "fix" the cherry eye but surgery. If he's uncomfortable around the eye, let the vet know and perhaps there is something soothing they can recommend to put in the eye.