I have a mossberg 500 GA 12 guage with select choke and the bolt stop is not functioning. How can I repair it?

SOURCE: How do you load a

The loading port is on the bottom of the reciever. You mention that it is "magazine ready"? Mossberg shotguns have a tublular magazine underneath the barrel, surrounded by the action bar and front grip.

Loading the magazine entails holding the shotgun in one hand, taking the shell in the other with the folded end facing the front end of the barrel. Place the shell in the magazine opening (on the bottom) and push it up with your fingers and forward with the thumb of the same hand. It will go completely forward of the silver/blue lifter and stay there when you let go. (the action must be closed to load the magazine).

Alternately, you can open the action and pop a shell into the ejection port on the right side, close it back up, and shoot!