How can I open and clean my head lamp that is covered with fug?

@chy4austin you cannot. Those lenses have most likely lost their protective film because of UV rays from constant exposure to the sun and harsh chemicals. There are plenty of products that promise to fix this issue but none of those will ever really work or replace the protective film. For a proper lasting repair, you would most likely have to replace the headlight assembly.

Sometimes the fog-look on headlights is on the outside. There are many ways to improve or restore their condition.

Here's a video tutorial on how to improve the situation using toothpaste. He shows you what it'll look like in the very beginning so you can have an idea of how much it might improve the looks. He also mentions that there are kits for sale for $15-20, and they're honestly the same stuff a repair shop would use. I will say that whatever you do, be careful not to get it on anything but the headlights. I used a kit once in an auto shop class and we had a fun time trying to get the polishing/cleaning paste off of the paint part of the car. Masking tape is your friend.

This video goes more into depth on the options for cleaning the outside of the headlights, comparing and explaining as he demonstrates them. At about 3:35, you can get an idea of the range of splash from a DIY kit.

If it is on the inside, here's a video that covers how to clean that without taking the headlight too much apart using magnets and cloth. He actually gets to the cleaning part at around 9:40.

You got this!