I disagree that the Iran Hostage Crisis needs to be avoided entirely. No, it simply has to end at an opportune time. Initially, the crisis engendered a kind of rally around the flag effect that was actually politically beneficial to Carter. If the crisis had ended at the right time, the hostage situation may have actually improved Carter's chances. The challenge is having it end at the right time. It's too bad you made the point of divergence in August, since that means you can't simply allow Eagle Claw to succeed despite all improbabilities.
August 1980 is probably too late to save Jimmy Carter, the best hope he has is simply not appearing at a debate. Let's say Reagan doesn't agree to debate without Andersen, and Carter simply refuses to show up for a debate. I remember reading that Reagan only emerged as the inevitable victor after that debate, and that indeed, Carter actually may have had a slight lead. Without the debate appearance, Carter's team may have an easier time painting former Governor Reagan as unpalatable extremist. And if Carter did indeed have a slim lead before the debate, there's at least a slight chance he keeps it. Now, no debate is probably as likely to lead to a smaller Reagan victory as a Carter reelection, but there's at least the slimmer of a possibility that Carter wins it by the skin of his teeth.
Again, ideally you want an earlier point of divergence, with the Iran-Hostage crisis ending at precisely the right time. Long enough to create a rally around the flag and support the President effect, but not long enough to make President Carter look even more hopelessly incompetent than he already did. Not sure what that time frame would be. If that were combined with a missed debate, Carter's chances would have improved immeasurably.