Hi Deactivated user...
I don't think there is a way to move question banks from a course back to the Question Banks at the account level. I tried looking for a way to do this in our own Canvas instance, and I didn't see any buttons to allow me to do what you were asking. Sounds like something that might be worthy of a Feature Idea, though. If you want, you can submit your idea here: Canvas Feature Ideas. Hope this helps!!!
@chofer is correct. The questions cannot be moved from a course to the account level, however they can be moved from a course to Canvas Commons. If your school does not have Canvas Commons please have your Canvas Admin ask your CSM. Commons will allow you to store content to pull into other courses and more!