If the headlight only has moisture in it, you can clear this out yourself using a hair dryer.

You will need to work out where on the headlight the moisture is getting in. This is the tricky part. Its usually via the seals thats cover the bulbs/globes. Check for gaps...if none, then it maybe the actual headlight seal around the glass where it meets the plastic. This is a little harder to seal back up (there are youtube videos on different ways to do it).

Once you've sealed it you basically face a hair dryer blowing hot air into it via the bulb/globe part of the headlight. Works a treat but takes about 30 mins or more to fully remove all moisture.

Hope this helps a little....and yes I've personally done it on my friends car and it does work