Need some heip with this, please. The YouTube video posted 3 years ago and the manual that came with the gun both show that you stick a screwdriver or choke tool in, depress it, and rotate it about a 1/4 of turn clockwise. Tried that, doesn't work. My gun has a small indention (?) on the underside of the tube that seems to be preventing me from turning the plug the 1/4 of a turn. Question - am I supposed to depress that indention at the same time I'm turning the plug, or does it snap out, or what? Any and all suggestions and help are appreciated. Thanks.