If you need to edit a purchase order after it has been submitted for approval [PA], has been approved [PO] or has been closed [CL], you can reset the purchase order.
PLEASE NOTE
In order to edit the closed purchase order [CL], it first needs to be re-opened [PO] and then reset [RE].
If the Reset option is greyed out, it indicates a the the PO is matched to an invoice. In this case please remove the purchase order link from the invoice. Learn more.
HOW IT WORKS
STEP 1: Open the details view of the purchase order
You can select the purchase order either by double clicking on the line or the pencil icon.
STEP 2: Reset the purchase order
Go to 'Action' dropdown and select 'Reset Purchase Order'

Adding a comment is mandatory when you reset the purchase order. After you have added a comment, click 'Reset'.