Maintain stock gone catastrophic

Hello All,
we were using drop shipping at my company and then we changed our business to be a normal supply chain cycle, to solve this problem we unchecked the maintain stock box for every item we have in the system.
turns out this will not solve the problem but it made it worse.
all the items that we unchecked the maintain stock box in are included in estimates and Sales orders
so how we could undo the unchecking box in all the items and it automatically reflect in the the estimates and sales orders