Un-Picking Sales Orders
Un-Picking from the Classic Admin Console is done by navigating to the transaction from the home page or Search > Transactions. 
Once you open the Sales Order, you will click on Detail to the right of the document line that you would like to Unpick.
A window will be displayed with the details about the line. Click Delete.
A window will appear asking you to verify the unpick action. Click OK.
The inventory is now Un-picked and will be returned to the Bin from which it was picked.