Credit Note to the customer

Hi All

 I have created some of the invoicesof ,say, 30,000 to the customer but now the customer is asking some discount , say,5000, and said to send the credit note on the whole invoices. Can anyone tell me how can i do this in AX, the procedure, do i have to use the "Free Text Invoiceing" and while selecting the customer, i have to select the customer account of the invoice account customer.

please advise

 thanks