Call your Senators, Congressman, State Rep, anyone with a D in front of their name. Tell them you've lost confidence in Biden and want the party to pressure him into stepping down before the convention. Then we can hold a contested convention, where the delegates will probably take several rounds of voting to decide a candidate. It's risky, but not as risky as doing nothing. It would also steal the headlines from Trump for a least a few weeks, which could build some momentum for the new candidate.