Search for threads where enterprising individuals upgraded their standard headlamp assembly to a projector system. To install a projector and the associated guts, they had to get creative in heating the assembly to remove the transparent portion, and then reseal it after the mod.
I do recall some pics at one time (on this forum), but that was a long time ago.
Nobody I know of sells the headlamp seal repair in kit form any more.
I had a Corolla with headlights that looked like a rain storm was inside.
I drilled a small hole towards the top outer sides of each headlight. I used a 1/8" drill bit and covered it with fabric tape from a first aid kit. The hole let moisture evaporate out from sunlight and from the bulb heat and they never filled up with moisture again. The tape kept out bugs and dirt from entering. Just get good 3M first aid tape that won't peel off. Mine lasted over 6 months until the car got totalled in an accident.
Make sure the hole is accessible to keep putting on fresh tape if needed. Mine had easy access when I removed the turn signals.