its easy no need to put it in the oven, use a heat gun and then re-seal it back tight with a good silicone product so no moisture will get in.

 

If you're talking about the black covers that go around eveything but the bulb areas of the light's...here's the thread.
All the links to the pics are dead but maybe you can contact the original poster and he can send you the info..

https://www.f150online.com/forums/sh...hreadid=150806

 

a heat gun will work also