If you found out that the quantity has been shipped incorrectly, you can undo the shipment if the quantity is not invoiced yet. To undo the posted quantity:
1) Open the Posted Sales Shipment.
2) Select the line that you want to undo.
3) Click on Function --> Undo Shipment
4) Click on the Yes button.
Navision will insert a corrective line with the same -ve quantity of the original line. A checkmark is placed on the Correction field in both lines to indicate this lines have been reversed.
Navision will also reverse the Quantity Shipped and Qty. To Ship fields in Sales Order. Therefore you can post the shipment again as the sales has never been posted before.