First, to return it, you need to receive a negative quantity against the PO.  If you are not actually going to return the motor to the vendor but keep it in stock for a future order, then edit the PO to remove the WO number from the line and re-receive the motor to stock.
 
Once you have unreceived the motor from the WO, you will be able to use WO-K-B and remove the line from the WO BOM and add one for the correct item.