How do I get this off the wall safely

New house, noticed the mirror coming off the wall. Can't seem to loosen this, it's about a half inch from the wall and I can't barely get a pliers behind it. Second pic is the holder from behind as best I could.

Any advice is appreciated, ideally I'd like to reset this with heavy toggle bolts in the same position as it currently is, left side appears to be in studs.

Thank you