When you initially access the Bills menu from the Customer Overview menu, you will see:
From here, you can see all bills that have been sent to the customer. Click on the bill ID in the left-hand column and you will see detail about the selected bill:
You can now view the actual bill by clicking View Bill, or void the bill by clicking Void Bill.
When you click on View Bill, you will see the same billing detail the subscriber sees:
If you click on Void Bill, you will be asked to confirm your action:
Select Yes and then click Process. You will see a success message (Processing Complete) in the lower right corner of your screen. The bill screen will appear: