How do you fix prelit Christmas tree lights?

The make bulb testers. Are you sure it might not be a fuse? Check that

first the work up to the lights.

I've often wondered what to do if you

bought a prelit. That's why I won't, it's easier to replace a string than find a burnout.

Also check to make sure the bulbs aren't loose.

Christmas light tester/I have this one

http://www.christmas-decorations-gifts-store.com/s...

I had that issue with my pre-lit tree. The problem with my tree was that not all the lights were plugged in properly. So once they were all plugged in properly they worked. Check that the fuses are also good in each set of lights. Make sure that the tree is unplugged when you are checking all these things so you don't get shocked.

look near the female end or male end of the plug in then it should have a little compartment open it take the fuse out and take it to lowes and tell them u want a replacement if that doesnt work just add a new strand and find a way to take the old 1 off

no not really, sometimes you can see dark tip or broken filament but not always