The wheel centre caps I had were stuck. I found this suction cap on the end of a toy arrow worked best.
First I tried getting the cap off with my fingers as others on YouTube had managed. But I couldn't get enough grip.
This suction cap worked well because it was smaller than the cap and could get a good seal. Other suction caps could come from GPS mounts, toys, etc.
After only a couple of tries it worked!!
If you are having no luck with the suction cap. Another method is to use a strong tape. Join the middle part of tape together so you have a tab to pull on (using pliers to pull is best).
This is how you stick the tape. I can't demonstrate this in action because the tape wouldn't stick to my caps. I tried gaffa and 3M and neither worked. I think it depends on the surface of the cap.