Hi SupportGuy
To add to what Tech Support writes, you can't modify a completed line, so their advice helps you in the future but not with this order. For this order, you will have to re-enter the item onto the same order. You can ignore the fact that the item already appears and was never shipped; there is no negative effect.
As another possibility, many Adagio consultants (maybe even yours) own a tool which can "uncomplete" a completed order detail. The tool is called Adagio GridView Read/Write, and while I wouldn't recommend it to the average end user because it is dangerous in the wrong hands, it is available for sale.
Steve