To add a good or service to an issued order navigate to Financial Management → Order Management. Next to the order you want to edit, click on Manage installments and payments, from here select Reopen:
Now that the order is reopened under the box Adding goods/services or discounts to the order you can choose from the drop-down menu the good to be added to the order. Click on add new catalog items to the order:
Now the new row with the added asset will appear in the order. It will be possible to change its price set it as payment out of installments or set the installment due date:
When everything is correctly set click on Save changes set to the order:
Click Continue on the pop-up that will appear to confirm the changes.
Now the order will have been correctly updated.