In 'Settings/Users/Access management', enable the right : 'Display the Return/exchange button on closed sales'.
Locate the initial sale from which the product is returned.
Click on the 'Return/Exchange' button.
In front of each product, you will find an 'Exchange' button to generate a credit note.
If the product returned is tracked into inventory, it will be automatically returned into inventory.
The credit note has a single ID number (single use) and you can print it as a barcode. The credit note has the negative price of the product returned and the same tax rate.
Consult pending credit notes in 'Reports/Pending credit notes'.
Create a new sale (=refund sale).
Add the credit notes generated after the return:
The refund sale is negative. Validate the sale with the payment method used to refund your customer.