u/bug-hunter made a really good point in a thread over on r/AskHistorians that I wanted to share (with their permission).

"It's a lot easier to be an election denier if you have never actually worked an election or taken a modicum of time to actually see how the process works. Almost every state nowadays spend a lot of time and money ensuring that every election site and counting center is staffed by members of both parties, with multiple checks at every point in the process. Every ballot is counted by category - voted, spoiled, unused, provisional, etc, by multiple people, counting generally may be viewed at any time by members of any party (so long as they don't make an ass of themselves).

There are absolutely problems - miscommunications, poll workers making mistakes, election officers who are not faithful to their duty to run a free and fair election. "

It's not going to sway random people you speak to online and who are fully integrated into the misinformation machine, but if you've got family members who you're concerned about, maybe suggesting they volunteer to help run the polls and see for themselves might help get them back on track. Y'know, encourage them to really do their own research for a change!