What should I do right now to stop it?

It's never fogged up before and just started yesterday...

The other rear light fogs up time to time but the previous owner drilled a hole so it vents pretty fast... Although a lot of dirt has made its way in...

Anyways what should I do before it's to late?

 

I had this problem with my car when I first bought it, took off the light used a blowdryer to dry it out and put a light grease around the foam seal, havent had any condensation sense then.

Only problem is I have water spots on the inside of the light from where the water dried I suppose I could use some distilled water to get rid of the spots or something.

 

It happened to mine a while back when it rained almost non stop the whole week. Anyway, i blow dry the water inside the rear tail lights and added a new and better gasket to keep the water out whenever it rains again that much like before. For now, it's dry like a newly put on pampers...lol