No one is asking the election be undone. He won that part fair and square.
He needs to prove he is eligible.
If the electoral college got together and voted for one of the Olson twins, we would have exactly the same problem. Some steps would need to be taken at some point in time to make sure whoever they elect meets the Constitutional requirements.
If a President shall not have been chosen before the time fixed for the beginning of his term, or if the President elect shall have failed to qualify, then the Vice President elect shall act as President until a President shall have qualified; and the Congress may by law provide for the case wherein neither a President elect nor a Vice President elect shall have qualified, declaring who shall then act as President, or the manner in which one who is to act shall be selected, and such person shall act accordingly until a President or Vice President shall have qualified.
There was the consideration during the amendment processes that we may have a case where a person was 'elected' but failed to qualify. In other words, something like what may be happening here wasn't out of the realm of possibility.
No, that's exactly what they are doing. That is the practical effect of what's happening, and all the semantics in the world won't change that.
I mean this absolutely seriously and with a straight face: pray for aliens to kidnap him. It's more likely.