What to do when Air Tag doesn't open with both thumbs?
Air Tag will not open / turn while pressing down with both thumbs; need to replace the battery
[Re-Titled by Moderator]
Have you tried wearing rubber or latex gloves for this task? Be sure to press & hold down the cover before turning it counter-clockwise.
Ref: How to replace the battery in your AirTag - Apple Support
If you are still having difficulty removing the read cover, it may be because the battery is swollen.