That's part of what the bill addresses. The wording would stipulate that a state legislature can't just use the claim of "fraud" as a pretense for overturning the tabulated election results themselves and installing a chosen candidate.

Now, if you're asking what would be done in the event that ACTUAL election fraud *is* indeed taking place somewhere...that's a tougher matter to preemptively legislate, because so many hypothetical scenarios could play out that lead to the evidence of such fraud coming to light in the first place.

What the LEVITY Act would do is prevent a legislature from, for example, saying, "Oh, we think there was probably fraud in this race...so we're going to install Candidate X into Candidate Y's seat while we 'investigate'..." (when, in fact, the hypothetical investigation is nothing more than a kangaroo court)