Rust under protective vinyl

[ChefRex]

Washing my 18 Colorado this morning and they have a protective vinyl sheet before the rear flairs, looks like some a**hat, clipped it in that spot is there is a scuff behind it that should come out no big issue there but under the vinyl there is what look to be rust.
I'll remove the vinyl, starting to look like **** anyway

Looking for suggestions on how to treat it before it gets worse without painting.

 

[Sweetcorn]

The rust is already behind the paint, so no way to address it properly without removing the paint in area you see and the area around it, then all the proper steps from there.