If your headlights are badly faded, this would only be a temporary solution.
To properly restore your faded headlights back to their original condition, it takes a bit of effort because the top layer becomes yellow/hazy from damaging UV rays.
To fix them, you need to sand down the top damaged layer and finish them with a clear-coat. There are some ready to use kits available on Amazon. Here is one I quickly searched up for you: Headlight Restoration Kit
After you're done. You can use the plastic restorer on them to help with UV protection.