The bounding box is forever fixed now, and we can’t reset it, the way it is possible in the desktop (and there is a separate request for that: https://illustrator.uservoice.com/forums/931888-illustrator-ipad-feature-requests/suggestions/42167054-reset-bounding-box).
But it would be better to make it better— by giving a mode to freely rotate the bounding box the way we need, to zero or another angle.
One more button in the context panel, or a toggle we can get when hold the rotation handle (to display the rotation center) — either way will do.