Clean the headlights with a mild soap and water solution. This will remove any dirt or debris that may be blocking the vents and preventing moisture from escaping.
Apply a desiccant pack to the inside of each headlight. Desiccant packs are small packets that contain silica gel, which absorbs moisture. You can find desiccant packs at most hardware stores
Let the headlights sit for 24 hours with the desiccant packs inside. This should give the moisture enough time to evaporate.
Use a hair dryer to heat the headlights. This will help to evaporate any moisture that may be trapped inside. Be sure to use the cool setting on the hair dryer and hold it at least 6 inches away from the headlights to avoid damaging them.