If the sales order has been created but not yet approved (Pending Approval), you can still change the Fixed Usage Quantity set.
a. Access the sales order in Edit mode.
b. Click the line item with Fixed Usage.
Note: It may default to the next available row which is blank so click on the actual line item otherwise, when you click the Set Fixed Usage Qty button, you will get a notice that 'Selected Subscription Plan has no Subscription Plan Items with Fixed Usage type'.
c. Click the Set Fixed Usage Qty button.
d. Enter Fixed Usage window will pop up with details of the Rate Plan. Preset Usage Quantity is editable.
e. Change the Preset Usage Quantity.
f. Save the Enter Fixed Usage window.
g. Save the Sales Order.