The user noticed that after placing a Purchase Order (P/O) in their Production instance, they forgot to include one item. The P/O was currently in an "ordered" status already. The user wanted to know if they could somehow retroactively add in the missing item, even though the P/O is already ordered.

Unfortunately this is not possible. As the original Purchase Order (P/O) is already processed, the user will need to submit a new order for any missing item they need.