Replacing a follower on a 20 gauge

[Coldsteel 86]

I have a 20 gauge that I picked up at a pawnshop recently. Along with a 12 gauge. Sweet deal. The problem I’m having is with the 20 gauge. I wanted to replace the plastic follower. But when I take end cap off. It’s threaded inside. And I don’t know how to get that part off. I watched YouTube videos, but no one addressed the issue that I have. I’ve taken the 12 gauge apart no problem. If someone could help me with this issue. I surely would appreciate it. Thank you