I had to play with mine last year when I removed one of the keeper screws by accident.
Straight up... this is not a fun job. It’s tedious and time consuming. That said, if you take your time and try to keep from getting frustrated, you can do it. One other note... it sure helps to have a 2nd pair of hands to help when needed.
There’s a 2-piece brass “keeper” that locks on to the chain in the channel. It’s this keeper that has to be moved either up or down a link or 2 to get what you need.
The following YouTube link shows what I’m talking about. Never mind the project the guy in the video is doing... just watch and the pertinent steps you’ll need to take will become obvious. Good luck...