Gstr - 1

Hello All!!!!

I have filed the GSTR 3B for the month of October 2017 in its respective time period.. Also the amount of GST to be paid was paid for the month of the same was paid in its respective time period.. Now out of the Sale Invoices for the month of October 2017, 4 Bills have been cancelled by the Consumers and he instructed to reissue the same invoice under NON GST Invoice since the said services had place of supplied at SEZ - LUT/Bond. So please guide the respective step to be taken for filling GSTR 1 for the month of OCTOBER  2017. How to settle the differences of excess GST paid and filling of correct GST return??