A couple of options:
1. You can embrace the scratch, as you'll likely get more on the clasp. Consider it part of your watch's life journey.
2. Take it to a professional jeweler/watch-maker and have them refinish it.
3. There are various DIY methods to take out scratches. Lots of videos on youtube, here's one with a quick overview:
I personally like to use the Bergeon 2834-C fiber glass scratch remover for smaller areas. But for a scratch like the one on your clasp, the scouring pad technique shown in the video may give a more uniform finish.
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