It is disappointing how few technical questions receive a decent answer on this site.
Here is one I prepared earlier - I had exactly the same problem.
The fog units are secured to the bumper with three torx screws, and the lens itself by two plastic spring clips which can be opened with finger pressure.
Use a flat blade to separate the lens from the plastic body.
I used alloy wheel cleaner to remove the aluminium oxide gunk.
prime and respray with silver rattle can, use clear silicon to reattach the lens.