Refund of GST - IMPG in case of Exported goods returned before delivery

Dear respected members,

Our client made an export (without payment of tax) last year. However, before delivery could take place, some norms in that country changed. As a result, they rejected the shipment and requested us to modify the goods to meet the amended norms.

Upon reimporting the goods, the officer at the port imposed GST, which was reflected in our GSTR-2B IMPG section. At that time, the officer assured our client that the GST would be refunded later. Now, our client seeking the refund, but we dont know how to , in this type of case

Please advise and provide assistance.

Thank you.