Or people could actually go out and tell others to vote.

Sure. This has been the strategy for a while, and has resulted in likely Biden voters becoming less engaged due to genocide and the general percieved cognitive decline as of late, and Trump voters becoming more engaged with events like the failed assassination attempt.

Biden voters are largely going to end up holding their nose, while Trump voterd are largely going to gleefully show up in droves, if conditions continue.

I don't think this is a useful strategy, and will be a repeat of 2016.

I don't see just changing candidates doing anything; in fact, you'd probably get a 'where were all the primaries?' backlash

If the majority of people support swapping out Biden, I think you'll find that it won't result in fewer voters. The DNC could also organize an emergency Primary, too. Doing nothing is handing Trump the win on a silver platter.