I can help you with this, CGAccounting.
You can create a new account in the Chart of Accounts. Then, choose that account when you apply the discount.
Click Lists, and then Chart of Accounts (or CTRL+A).
Click the Account drop-down below. Then, click New.
Choose the correct account type, then click Continue.
Click Save & Close.
To apply the discount:
In the Customer Payment screen, click Discounts And Credits.
In the Discount tab, click the Discount Account drop-down and choose the account created.
You might want to check out this article for your reference: Record a credit memo or refund in QuickBooks Desktop.
Let me know if there's anything else you need.
... View more