I am not sure what you are trying to describe. Are you referring to the magazine follower, that little plastic piece inside of the brass magazine itself. If so, the follower is held inside of the magazine at the end by a crimp, If it is coming out, crimp the end a bit more to hold the follower inside. If it is the outer tube that actually holds the magazine, check the mount. There are a number of YouTube self help videos out there. A better description with pictures would allow us to help you further.
Had the same problem with my 1959 Golden 39A. Modified the outer tube pin groove to look more like a later model 60 style tube. It will help keep the locking pin from rotating where it can slide out when it is under tension from the inner tube spring.
I have read on several forums, and I have had a Winchester and a Marlin that the inner Mag Tube would come out really easy. The outer tube was fine. Just a very, very slight bow of the inner magazine tube and problem solved. Worked great on my two that had the issue. No problems now. You don't even want to bow it where you can see it. It takes an ever so slightly bow. This has been the fix for this problem over the years.