Gstr-1 filed correctly but 3b incorrectly

Hi Experts,

I have filed export sales figures correctly in GSTR-1 but i missed 1 export bill in 3B of July 18 returns and as a result of which our export bills are not transmitted to ICEGATE.

Please guide as to how to correct/add the missing bill in next return of Aug ? Do i add sale of missing bill in 3.1(b) of 3B or 9A of GSTR-1 ?

Thanks !