Get real folks.
If there is a change it will need to be before the democratic party convention in which Biden could simply withdraw from seeking the nomination.
After that before the election, the only way will be for him to resign from the presidency or die in which case Harris becomes president and also the incumbent.
In my view, the best chance to win (Michells has zero interest) is to go with Governor Whitmer who would likely sweep the Midwest and also Pennsylvania.