Credit Note is something which is provided by shipping providers in case of weight dispute or wrong charges.
In case of Credit Note shipping providers share credit note on mail for example in case of FedEx, FedEx team shares credit note on mail in PDF format.
Accounts Team can upload credit note through mis_reports_new entity in mystore.
For uploading credit note:
After that system automatically process that credit note to the user and you can also verify manually in the ledger of the user that credit note is successfully applied or not.