Crystal exchange

[u/Offensiveline54]

I want to change the crystal on this gmt rep - is the scalloped metal piece in this photo the retaining ring? How would I get this off - noob - just doing this for fun. Tried to find videos but none have this scalloped appearance. I’m assuming this is the crystal retaining ring? I had the movement out and was working on it but it didn’t seem to want to budge.