If you're trying to fix a string of Christmas lights, the first thing you should do is inspect them for any visible damage or broken bulbs. If you find any damaged or broken bulbs, replace them with new ones. Then, check the wiring to see if there are any frayed or loose wires. If there are any loose or frayed wires, you can try re-wiring the lights with fresh wire. If that doesn't work, you may need to replace the whole string of lights.