Hi @Samantha73 ,
You cannot directly undo a registered Warehouse Pick.
The simplest solution, if the Warehouse Shipment has not been posted:
Open Warehouse Reclassification Journal.
Enter the item and quantity.
Set From Bin to the shipment bin.
Set To Bin to the original pick/storage bin.
Select Register.
Delete and recreate the Warehouse Shipment/Pick if needed.
For lot- or serial-tracked items, use the same lot or serial number.
Kind regards
Tarik Jerković