Isn't it 'crushed' into place? I suppose you might have to get medieval on it to pop it out, then to reinstall get it in place while the frame is held vertical and tap ('crush') it back into place with a hammer and brass rod.
But then, I've never done it and wouldn't trust myself to do it. I'd contact some known shotgun gunsmith shops and have them do it. I learned long ago it was cheaper for me to pay somebody to do such stuff (rather than fix what I screw up).
One of the very best at any shotgun work is Phillips Gunsmithing in Emory, Texas. I'm sending him a trap gun to do some trigger work on next month.