Create credit note
Credit note is also known as credit memo, is a form or letter sent by a seller to a buyer, stating that a certain amount has been credited to the buyer's account.
A credit note is issued in various situations to correct a mistake, such as when (1) an invoice amount is overstated, (2) correct discount rate is not applied, (3) goods spoil within guaranty period, or (4) they do not meet the buyer's specifications and are returned
You can do this in two different ways.
Option A: On your dashboard, go to sales > credit notes or click on plus sign > create credit note