When you create a sales order for Item with substitution setup, Navision will place a check mark at the Substitution Available field in the Sales Order Line.
If the quantity that you entered in the Sales Order Line exceeded the available inventory, Navision will prompt up an message as follow:
Please note that the Substitutes Exists field is checked if the Item has substitute.
To substitute an item in the Sales Order Line with the substitution, click on
Line –> Select Substitution to open the Customer Item Substitution window. Select the substitution item and then click on the OK button. The item in sales order line will be replaced with the substitution item.