For the third time. In a court of law when you provide an affidavit you are swearing on the holy bible under penalty of perjury that your testimony is the truth. The court accepts this as evidence. Trying to contest that as a lie is damned near impossible way to defend a case. Unless you have medical evidence which diagnoses the witness as mentally ill, or you have rock solid irrefutable documentary evidence proving the witness is lying about what they saw, then their testimony is taken as a fact, not an allegation, not an opinion, not an unsubstantiated assertion, but a fact.
If the witness says they were asked to backdate ballots. Then it's a legal fact. You now need to explain why that is a normal procedure, or explain that it was just an isolated incident, or explain they misheard it and put them through a tough cross examination to make them doubt their own memory. Something. Simply saying it's made up is not a legal defence. Saying there is no other evidence to prove it, is also not a legal defence. The affidavit is proof.