There is information on the TIS CD about this but posting copies here is a bit complicated.
Basically......... They say that a bit of condensation is OK and it wil go away when the weather gets drier and/or warmer or you turn the headlights on or ..... or ..
Their threshold of worry is 2mm of water in the bottom of the glass!!!!!!!!!
To take the lens off:
1) remove the headlight completely.
2) release the top and bottom clips, which may be different dependent on the make of the headlight, and also different top and bottom so make sure they go back where they came from.
3) on ZKW headlights release the side holders
4) remove the frame with the lens.
Its as easy as that. If you want more with pictures buy a TIS CD off ebay.