So what would a plan look like?
For a candidate, a plan would involve being prepared to contest an election, before, during, and after. Before an election, a candidate needs to raise concerns of election integrity, needs to encourage people to vote in person on election day, and to protest changes in laws and regulations that make elections less secure and more vulnerable to fraud. If the candidate doesn't know what laws and regulations make elections more vulnerable to fraud, they should get advice, or drop out.
During an election, a candidate must point out that just because someone gets a ballot by mail, doesn't mean that they have to vote that way. Even in universal vote by mail states like California, a person can still return that ballot to the polling place in person, or simply cast a ballot in person on election day. They should discourage ballot harvesting, drop box use, voting by mail, and other fraud promoting actions. Make Election Day Great Again.
Before the election a candidate needs to assemble a team of good election attorneys and auditors, and have them ready to go before results are certified. If they aren't needed, fine, but they should be ready anyway with motions, audit demands, and other materials to file before the ink is dry on certifications.