You just have to switch the first and second future, the default future is the Biff timeline, then you have to change the future to make the hoverboard timeline.
That would actually be so cool but I can already see the scathing online criticisms:
"New WOKE BTTF2 ruins a family movie with vulgar dystopian future, not an ounce of original thinking in the writer's room. Entire second act of film missing as plot is resolved in only 1 trip."
Might be better to just stick to original stories and concepts, tbh.