[Mamma taught me it's not polite to pry]
Ignore if your gauges appear to differ from the TR gauges...
My bezels rotate off... looking at the back there are tabs that will align with notches in the gauge backing when the bezel is rotated. It may still feel stuck ot that point if there is a very old gasket in there that has stuck to the glass, bezel &/or body of gauge.
To get a better grip to rotate I use one of those rubber jar lid openers. If the gauges have been closed up for a long time the gaskets are possibly shot. I made my own from black gasket paper though replacements are surely available.