Refund of export of goods

Hirav Panchal (20 Points)

19 October 2018  
Client made export in the month of May 2018 including IGST. I filed GSTR _3B and showing export in table no. 3.1(a). As I was not received Shipping details in qtr ended 30th June 2018, I filed GSTR-1 of quarter 1 without including shipping details. So my export invoice not transferred to ICEgate. Now how to correct gstr3b and gstr1 to get IGST refund.
plz advice me. Now I have shipping details for said export.