Pull the fender.
Sorry I just couldn’t resist.
If this is the Tahoe, I’m assuming it is because you are asking us. But we all know what you do when you assume.
Unless there are screws on the marker light itself you will have to get at it from behind. Anything that is in the way move out of the way.
I know we have a few Tahoe owners on here that may be more familiar with this than I. be patient some are not on as often as others.
Believe me I know your pain with the weather. It’s been down in the 20’s here lately.