There's a two piece metal bracket, (two plates), on each side, one piece inserts into the boot at the base of the turn, seen in your picture. The second plate screws into the inserted plate and keeps the turn in place in the fairing. Both are best inserted once the turn is in place in the fairing. You might be able to reach up inside the fairing from the outside or you might have to take the front fairing off to do it. It's been a long time since I had a 500 and I don't exactly remember.
The front fairing is easy to take off if that turns out to be the case.
07 HD Nightster