Take the headlight out from the car, remove the bulb then simply pour a table spoon of methylated spirits into the inside of the lens.
Swirl it around covering all of the lens. Turn it upside down, drain out then sit the headlight in the sun to completely evaporate all the meth spirits from within the lens.
You may have to do it 2 or 3 times.
I've done it and it works. GL