First try cleaning it with a good microfiber cloth. Then maybe a moist (not wet) cloth. I'd try a tiny dab of mild hand soap, but that's me. If there's no change, then try Apple. They may exchange it, but don't be surprised if they want to send it in for repair.
My 2015 MB slowly developed some spots on either side of the trackpad, obviously from my hands. A solid wiping with the microfiber cloth cleaned that right up. I'd never use any like of polish or heavy duty cleaner as that might react with the finish.