What if a jewelry repair store damages your jewelry?

First step would be to ask the Jewellery store if they will repair it.
I expect most Jewellers would do happily do so. If they say it cannot be repaired, then I would ask them if they would compensate you by buying the Jewellery from you.

If they refuse to repair or compensate you, you will need to research what consumer rights you have in your country. An internet search for "consumer rights" and your country name should point you in the right direction.

Even if you had been advised by the Jeweller (verbally or in writing) that they do not warrant the repairs, you may find that you have certain statutory (legal) rights that override that. You could remind the Jeweller of your rights, and ask for repair or compensation again (perhaps in writing).

Many countries have a system like a "Small Claims Tribunal" - a sort of express legal process for remedying consumer disputes. Again, an internet search for "consumer rights" and your country name should point you in the right direction.

Best of luck. If all else fails, try another jeweller. They may want to buy the Jewellery from you if they are able to reuse the parts.