Dust cap stuck

[JudeBytheway]

The rear dust cap is jammed on my Control Ring Mount Adapter EF-EOS R. I accidentally put on an EF mount dust cap without realising. I did not use force to do it, but it won’t come off. It will rotate a small amount each way. How do I remove it? I need to get it off ASAP.

[Tronhard]

I would suggest wrapping the dust cap that is stuck in something very warm - perhaps heat a flannel in a microwave and then wrap it around the dust cap. Just make sure you don't contact the adapter. The heat should expand the hole and hopefully allow you to wangle it off.  That is the least intrusive thing I can think of...