Here are a couple of articles that might be of help.
http://www.woodcentral.com/bparticles/save_finish.shtml

https://www.popularwoodworking.com/techniques/finishing/rejuvenating-old-finishes

You can get rid of the water spots with Jasco or Homax White Ring Remover cloths.

I have removed water rings from many types of wood furniture by using an iron. Place a smooth absorbent cotton cloth (like a tea towel) directly over the stain and with a dry iron (NO
STEAM!) press down for several seconds on the cloth. Remove and check
the stain. Keep doing until the watermarks are completely gone. It could
take a minute or two to get the stain out completely. My mother was going to refinish her kitchen table until I removed the rings. Now it looks fine.