I’m not clear whether you are trying to polish both the epoxy resin
and the bezel, or just the bezel.
If the former, you need to use different polishing compounds and
techniques for each. Epoxy can be polished, though it will bear
minute scratches from the process. It’s best done under water with
two or three grits of fine sandpaper, like 400/600/1200 and then
finishing with a Fabulustre-type rouge. Don’t use colored rouge, as
it will stain the epoxy. You can use polishing sticks, cloths or
buffs on a flexshaft. If you use the flexshaft for the final polish,
run it real slow and keep the surface watered. Be careful not to
overpolish; the resin can be quite soft.
If you are trying to avoid touching the epoxy and just polish the
bezel, little rubberized wheels and masking tape work well.
As to tumbling, the only medium I’ve found that’s reliably safe on
epoxy is dry corn meal.