Article 1, section 5 clause 2 says it take a 2/3rds vote to expel a member. I can’t find where it says anything about removing a member with a simple majority. My Constitution doesn’t have a section 5 in article IV; it stops at section 4. Is the simple majority rule in that missing section? I think that wasn’t ratified, except maybe in your head.
That is after a trial in Congress. But fraud vitiates everything, putting the member in question at a state before they were sworn in, so a declaration by state Legislature of fraudulent election and quo warranto motion referencing the fraud should be sufficient. They don't have the authority to present themselves for induction into Congress. So Congress only needs to pass a resolution and ignore them until the election is corrected.
IANAL - I am not a lawyer. But we all need to be Constitution literate because our kids need to be able to read it as well. Note that the US Constitution is written in script, which is no longer being taught in schools. Thank you Dr Franklin!