1. Go to the Billing & Collections section of the customer account.
  2. On the Bills tab, hit the Options button and select Reverse Bill.
  3. Confirm that the bill should be reversed.
  4. Click OK and the transactions on the bill (statement) are reversed and reapplied to the Unposted tab.

Sometimes bills (statements) cannot be reversed because of the time limit set by your company to modify the billing information.