It is a good practice to create draft credit notes when doing full or partial refunds, especially when you are still practising how to use the credit note functionality and learning the workflows. Draft credit notes can still be edited or completely deleted if you have made a mistake.
Just like with original invoices, finalised credit notes cannot be edited or deleted. When there is an error on a finalised credit note, you must create another credit note for the credit note to correct the error. Creating a credit note for another credit note is done in the same way as creating a credit note for an invoice. Note that the 'Credit and invoice again' option is not available when crediting credit notes.