Changing the quantity or removing the quantity of a SKU in an FBA shipment in Monsoon Marketplace can only be performed on an open FBA shipment. Zero out the FBA quantity in Monsoon Marketplace and it will no longer be included in the shipment. More information can be found in the FBA section of Monsoon Marketplace Help.
If the shipment is closed in Monsoon Marketplace and you modify the quantity of an FBA SKU directly on Amazon, the shipment items cannot be changed or removed in the FBA shipment in Monsoon Marketplace. If you would like to list these removed items locally, you will need to receive them into Monsoon Marketplace with a new SKU.