How to file GSTR1 if opted to file Quarterly GSTR 1 retrun ?

Option of quarterly filing was not available earlier,

•  Many taxpayers have already filed their FORM GSTR-1 for the month of July, such taxpayers shall not file these details again and shall only file details for the month of August and September, 2017.
•   For those, who have not filed their FORM GSTR-1 for the month of July, they shall also file their FORM GSTR-1 for the month of July separately and then file their FORM GSTR-1 on quarterly basis for the month of August and September, 2017.

[Circular No 26/26/2017 GST Dated 29th December , 2017  ]

Due Date of Various GST Returns : Notification wise, Month wise & Form wise 

Related Topic on GST