Rule 96 - IGST Payment of Export related credit note how to shown in GST Return.

Dear sir /madam,

At the time of export, we paid IGST and also declared in GST return that related invoice details. Based on return CUSTOMS Dept. refunded IGST amount against invoice number and shipping bills details.

Subsequently, we received one credit note against that invoice (WITH PAYMENT OF IGST EXPORT invoice). In GSTR-1 portal can't permitted to adjust the IGST paid related invoice.

My query is how to shown this type of credit notes in GSTR-1 and how to discharge IGST amount. Kindly suggests..