Rectification of gstr-3b once output liability has been set off and the same has been 'submitted'

Today (18-09-18) while filing GSTR 3B for the month of Aug 2018 i mistakenly entered IGST as eligible ITC though I have no ITC for IGST. Consequently while setting off certain amount of the wrongly booked ITC of IGST has been utilised towards payment of my Output CGST and Output SGST. Kindly help me out as to how should I rectify the mistake.

Thanks.