What to do if my self harm scars are visible during an interview?

yeah if they ask during the interview then you shouldn’t work there and report it to HR

They're not allowed to ask about your medical history beyond if you'll need any accommodations to do the job, if they do ask that's a red flag

If they ask, tell them politely that it's not their business to know.

Chances are, they won't. Do you make up that can cover them? Or maybe some accessories?