The mirrors are usually held into a tapered socket. After a while they get stuck. Put the big bolt back in, but about two turns loose. Whack the head of the bolt hard upwards. That should loosen the arm in its socket.
Putting some penetrating oil in the socket for a few days first would probably help, too.
This is what I've done, and it works, but you have to be careful; too much force could break something.
I've also found that a big rubber hammer can sometimes break the mirrors loose if you use penetrating oil first for a few days.
Tom & Jan ---- Westwing43 (RVM28)
2008 NEWMAR MOUNTAIN AIRE 4528
Pulling a 2014 CHEVY CAPTIVA