The plan should be general strike or something, but because the Dems already won by preventing Bernie from getting the nomination they don't actually care who wins between Trump or Biden that much. Sure they would prefer Biden, but at the end of the day the main goal has already been achieved. That's why the democratic party isn't planning any huge resistance even though Trump stealing the election is a very likely scenario. Remember the Dems are basically controlled opposition designed to be the graveyard for social movements and change, and to absorb anger at the current state of affairs.