I feel for you man!
The brand-x adapters with the removal tool have a tendency to get stuck on the cameras. I bought one and spent over three hours attempting to remove it from one of my film cameras. That is why queries on this site regarding adapters are usually met with a chorus of comments suggesting the genuine Pentax item. It costs about twice as much, but the savings in frustration are worth it.
I wish I could tell you a magic formula for getting it off, but I don't know one. I just fiddled with it for several hours and when it finally released, it slipped off quite nicely with no effort. Did I put it back on? No!
Assuming that you are eventually successful in removing the thing and are interested in redeeming it, here are two methods of how it might be done:
#1
Remove the offending spring clip with a fine-tip screwdriver. This will defeat the locking mechanism so the adapter will be free to rotate off the lens. Some forum users have used a Dremel tool or a small drill on the mount face of their M42 lenses to engage the k-mount retaining pin to avoid the lens falling off.
#2
It is possible to modify the contour of the bayonet "ears" so that they more closely resemble those of the genuine Pentax adapter. This is done with a small file or Dremel tool and is supposed to make removal more consistently possible. There are instructions elsewhere on this site on how this is done. With any luck, one of the people with experience on this will weigh in their comment on this thread.
Edit:
I found the thread for fix #2
https://www.pentaxforums.com/forums/camera-studio-accessories/53064-m42-adapt...s-generic.html
Steve