Which step would a Business Practitioner take to process a refund on an order that...

According to the Adobe Commerce Merchant Documentation, you can process a refund on an order that has been invoiced by creating a credit memo. A credit memo is a document that shows the amount that is owed to the customer, and can be applied to the customer’s account or refunded to the original payment method.

References: https://docs.magento.com/user-guide/sales/credit-memos.html