In the CS-Cart admin area:
- Go to Orders
- Search or browse for the order you want to edit.
- Click on the order ID or click View
- Click on the Edit Order link on the View Order screen
- On the "Products" step, Click on the "Proceed to the Next Step" button.
- On the "Customer Details" step, Click on the "Proceed to the Next Step" button.
- On the "Totals" step, check the "Order discount" checkbox and enter the discount amount. Then click on the "Proceed to the Next Step" button.
- On the "Summary" step, click on the "Save" button.
The order should now be saved with the discount applied.