If the scuff are actually scratches in the plastic then you would have to clean the area with some diluted APC and try to smooth the plastic back out to match the surrounding area. You can try this with a very light scuffing pad, like the back of a kitchen sponge. If you try this do it with both surfaces damp. Otherwise you can try a trim treatment like Black Wow, Wolfgang Exterior Trim Sealant. It all depends on how deep the scuffs are. Usually you can try darkening them, but they are usually there to stay. If you try to scrub the plastic you could distort the area more than you want. I would stick to cleaning it thoroughly with a mild APC and a light scrubbing pad(maybe try a magic eraser) and then treat the area with a plastic treatment/protectant that will darken the scuffs again.