Left ear bud wont play music. Where can I fix them?

Have you tried it in multiple devices? I wouldn't recommend repairing it if it can be covered by warranty. The site was down when I tried but you can go here: www.beatsbydre.com/support/beats_warranty,default,pg.html. You can also try the original place of purchase and exchange it.

If it is physical damage and they won't cover it, contact local cell phone repair shops and see if they can take a look.

Good luck!