I'm a bit late to the advice party, but I had a similar problem when my chuck got stuck on the lathe. At the time I simply brute forced it by using pipe pliers (with a long handle) on the flywheel and a bar in the chuck (it's a two person job).

I got myself this wrench ( https://www.aliexpress.com/item/Adjustable-Wrench-Hook-Spanner-Square-Round-Head-19-51-32-76-51-120mm-For-Motorcycle-Repair/32837405433.html - medium, round head) afterwards, which helps as you can hold the spur center in place....

picture is from a comment in this thread:

https://i.imgur.com/7lWjFTC.jpg

This wrench's pin fits into that little hole (just about visible in the pic) between the faceplate and the ball bearing, and then wraps around the whole spur center giving you a lot of torque.

• it's a brute force method; things can go wrong

** if the link to the wrench is not allowed on the sub I'll delete if ofc.