>>How does he know who they voted for?<<
Two points: First, they might be registered with a party.
But the main point is that if they can show it was a fraudulent election and that the fraud was of sufficient scope to affect the result, regardless whether it actually did, a judge could throw out the result and decide upon a remedy. That could be a do-over in certain precincts, or the whole state, or toss it to the legislature to decide on the electors.
That said, I’m skeptical that they’ll have the evidence, even though I think this election was stolen.
Maybe they voted in person and absentee- or perhaps voted in Nevada and another state, which can be documented. Or both!