If the medium detects that a spirit is present, he will try to convince it to move on. How effective is this? It's hard to say. Sometimes it works, and sometimes it doesn't. I often get calls from people asking for this service, but in my years in the paranormal field, I have found very few people trustworthy enough for this assignment. They are out there though, and your investigator should do all they can to get you in touch with them.