Now that's a great question to ask and it seems that no one has an answer for that. I have the same problem with a stone that hit that plastic piece and made a very small scratch. I've been looking online and no one seems to have anything.
If it’s a piece that’s black on all color cars then it’s just plastic (the body color piece on the fake vents for black crystal pearl is painted black crystal pearl).
I tested some plastic polish on the outside glossy black perimeter of a fake vent and it worked fine.
Bumping this back up. So, my brand new 2021 FK8 already has scratches in the rear bumper black plastic trim pieces. I am wondering how in the world people are keeping it clean without scratching it? I am also wondering if I can use an orbital polisher on it to remove the scratches? Very frustrating...
You should be able to polish them out with a DA Polisher. light polish as its plastic, and light pressure.
I have been trying to minimize touching those panels as the piano black will show swirls BAD, but I have had luck polishing piano black trim in the past.
If you do not have a DA, you can use a hand applicator, it will just take a little more time, but you should see improvement.
Hey i know the black trim pieces are very hard to keep nice but you can polish them i do it with a dual action polisher and begin with a light cutting factor polish and see of that does the job. Also be carefull not to polish too long at the same place its plastic.