Received payment from customer. Several of the invoices listed on the payment advice had incorrect amounts, resulting in an over payment. The over payment was left as un applied amount when the payment was completed. If you view Received Payments in customer information, the un applied amount is listed.
How do I convert this un applied amount to a credit memo that can be provided to the customer?
I've got your query covered on how you can convert an overpayment into a credit memo.
This option to convert a customer's credit to a credit memo isn't available. But, QuickBooks automatically recognizes the customer's credit and provides you an option of either retaining the overpayment amount or apply it to a different invoice.
In case the customer in question doesn't have any other open invoices, you can apply the credit to their future invoices. You'll see an Apply Credits option on every new invoice.
If you're looking to issue a refund, you can view this article for details: Record a credit memo or refund in QuickBooks Desktop. You'll find two sets of steps on how you can issue a refund. It also has the steps for how you can create a credit memo or refund for MAC systems.
I'll be here in case you have other questions. You can leave them in the comments below, and I'll be sure to get back to you.