Forgot to say, heat for 10 - 15 mins only. This will unset the sealant around the headlight surround. Clamp ad allow to cool for 20mins. This should only be performed if your lights have vents. If not you will have to remove the cover. Check for screws and pull out from one side to another. Left to right or right to left. One continues movement and avoid contact with plastics.
Clean inside with lint free cloth, do not use any cleaning product, if your head light has a chrome plates insert this can be removed for better access and is usually held in with clips only.
When reassembled, heat light again and clamp closed as described before.
Light should be centered in the oven with no part touching the sides, top or bottom. Preheat the oven before placing head light inside for hearing.
Might be worthwhile installing Halo's while your at it, or easier to replace light with a new one