More information on how to manage credits on a customer's account including the ability to manually add or subtract funds can be found in the Manage Credits Documentation
The credit reports allow you to run both a current balance report (Credit Summary) and a detailed Credit Transaction report to view and manage customers with credits saved on account.
Credit Summary: The Credit Summary report allows you to view the initial and current credit balance of all customers who have credits on file. Learn More >
Credit Transactions: The Credit Transactions report gives you a detailed summary of all credit transactions (Additions, Subtractions, Order transactions) for a given date range. Learn More >