You file suit. In federal court. Then the presiding judge decides whether your case has merit, a jury is selected, and a trial follows. Then the "civil servant" who violated the SCOTUS ruling and, in the process, deprived you of your rights, gets a multimillion dollar judgement against him. Or her.
They probably offer to settle somewhere along the line. You smile and say, "Nope," because your case is as clear as a mountain stream.
And every other "civil servant" in the country takes a look at the judgement amount and decides, "Nah. I'm good. I think I'll stop standing in the way of RKBA, thanks. It's not worth my kid's college fund."
That's how lawsuits work, in essence. The enforcement mechanism is greed, basically.
ETA: In before the usual suspects flapping their arms about BuT wHy WoULd tHE jUdGe LeT tHe TriAL PrOcEeD????" That's been answered many times. These are federal courts, and they're already siding with Bruen nationwide. Even the Dem appointed judges.