Don't know what key I used, but the TLR3 fits my P01 (urban gray) fine.
Took it off (hate doing that). The adaptor plate has only one marking on it. Looks like a "C" inside a circle. You can see from the picture the tab that fits into the slot in the pistol's rail is sticking out in front of the clamp. Took the clamping mechanism apart.
If the tab is to the rear: remove the screw, pull the right side clamping piece off the light, lift the adaptor plate out and turn it so the tab is to the front, line up the hole in the plate and the left side of the clamp, then put the right side of the clamp on the light, then insert the screw and screw it in far enough to hold the right side plate on. Then put it on the rail and finish clamping it down.
Oh, make sure the pistol is unloaded before you start mounting the light to the rail.
Good luck.