Purchased a used Late 2011 Macbook Pro and cannot get find my Mac to work. What do I need to do?

So I purchased a used late 2011 Macbook Pro from a friend. I am trying to get the find my Mac app set up but it won't let me because I believe he still has it as one of his devices. I texted him a couple days ago to ask him to remove it, but it doesn't seem he has or is in any rush to do that. I was debating re-installing the entire OS to give myself a fresh start. Will this give me the ability to set my computer up on the find my Mac app or is it tied to something more than the hard drive/OS.