Refund of igst paid goods, mistake in gstr-3b

One of my client have made export of goods with payment of IGST in the month of September, 2017. Subsequently, I have filed GSTR-3B, wherein, I have, by mistake, made entries in point 3.1 of GSTR-3B instead of point no. 3.2(i.e. Zero Rated Supply) now there is mismatch between GSTR-3B and GSTR-1, hence, I am not able to get refund.

I would like to know the procedure to get the refund, I have been to GST Department where jurisdiction lies but in vein. Any help shall be highly appreciated.

Regards,

Chintan Dave