Make sure the Invoices & Payments tab is selected and select
the invoice you want to base the credit note details on.
Press the dropdown arrow under the Convert button.
From the dropdown menu, choose To Credit Note.
The credit note will be
created and opened in a form allowing the details to be edited. The
form should look something like the following.
Edit the credit note as needed. Press the Close & Save button to save any
changes you make.