Exorcism

You attempt to perform an exorcism on a creature by touch. The target must succeed on a Charisma saving throw of 15 or higher

On three successful saves from the creature, the caster must start the spell over again and will take 1 D4 psychic damage

on three failed saving throws the demon will be expelled from the host's body and will be vulnerable to attack

If caster removes their hand from the creature, or performs a separate action they will break concentration and must start the exorcism over.