GST Department issued GST return offline tool version 1.0 for uploading invoice data and other records for filing GSTR-1. However GST department already gives extension for filing GSTR-1 for july month to September 20. But the department is no late issuing offline utility for filing GSTR-1.
You can submit your GSTR- 1 return now too and why to wait for last date.
You can download GSTR-1 offline utility tool from the link given below