How this works is that the house majority nominate and elect the speaker of the house. Traditionally it's a sitting member of congress, but it doesn't need to be. They can nominate/elect just about anyone.

And the speaker of the house is 3rd in line of succession for the presidency, i.e. if the president dies or is removed, the VP becomes president. If both the president and VP die or are removed, the speaker of the house becomes president.

It's expected that the Republicans will win back both the house and the senate in November's midterm elections. This is usually what happens in a first term president's midterms. And the Biden presidency is looking exceptionally unpopular, so the Republicans are going to do really well.

If they win the house, they can impeach Biden. If they also win a supermajority in the seantae (2/3rd majority) they can convict and remove him. Then they can do the same to Harris, making Trump POTUS again.

Best part is, if he takes over Biden/Harris' presidency, the remaining two years of that term don't count against Trump's term limit, so he can run again in 2024 and potentially be a 10-year president.