By doing what?
By doing whatever he thinks is necessary. He could declare martial law, send in troops to take equipment, do financial audits of the existing ballots, order new elections, make arrests, seize assets, whatever the President thinks needs to be done to put a stop to this treasonous behavior and cleanup the elections and restore his legitimate win.
But I'm not privy to what Trump would do. But he won't play footsies with these traitors. He takes a hardcore outlook on getting back at people who have wronged him. The democRATS outright stole this election from him and he knows it and so do tens of millions of other Americans. He's not a turn the other cheek kind of guy. He believes in vengeance.
I believe he'd do whatever is takes.