Quantities can only be altered somewhat once your Amazon shipment plan has been verified
Amazon FBA will only permit the number of each Amazon SKU to be modified up to 5%, or up to 6 units, above or below the initial amount without charging costs if you have already accepted a shipment plan.
You will have to duplicate the shipment or make a new shipment if you need to add more units.
You are not permitted to add more Amazon SKUs.