You may usually remove soil from vinyl with warm water and mild detergent.

Apply a small amount of detergent solution to the soiled area and let the detergent soak for a few minutes in order to loosen the dirt. Rub the area briskly with a clean, damp cloth in order to remove dirt and traces of detergent. You may repeat this step several times if needed.

Soil from such things as tars, asphalts, shoe polish, etc. stain if left on the trim. Wipe off these compounds as quickly as possible and clean the area with a clean cloth dampened with GM Tar and Road Oil Remover (GM P/N 1050172) or equivalent.