Just show up for the Sept 10th debate you already agreed to. ABC, don't cave to any of his weird demands/temper tantrum; just do the debate as agreed, and if he doesn't show, that's fine too.
People aren't going to want to watch three debates of your dumb ass in a single month. One debate is sufficient in September. If you both agree on it, one in October to keep it fresh in people's minds are also fine, though not necessary. Everyone knows Trump already, this is really just a chance for undecideds, or wall sitters to get to know Harris.