If a negative balance is added to a patron account, the following workflow can be used to remove it:
Retrieve the patron account and go to the Bills screen.
Select the bill with the negative balance, click on Actions for Selected Transactions or right-click on it, and select Add Billing.
A window will pop up that asks "Are you sure you would like to add a billing to bill 1234?" Click Yes.
A new window with the Bill Patron Wizard will appear. Select a Billing Type and enter in a positive bill amount for the same amount as the negative balance. For example, if the negative balance is -$35.00, enter $35.00 for the bill. Click Submit this Bill.
The negative balance will now be cancelled out and cleared from the patron account.