I have issued a credit note already, want to link our refund to the credit note
"Click the Plus (+) icon on the upper-right corner. Select Refund Receipt."
No, don't use a Refund Receipt; that reduces income which was already done with the c/memo. The account allocation of the Expense or Cheque should be Accounts Receivable (Debtors). Then create a zero Receive Payment to apply the debit to the credit