Is it possible to file GSTR 3B of oct 19 without filing GSTR 3B of Sept 19?

No u can't file without filing September 2019

No.
As per section 39(10) of CGST Act 2017, a registered person shall not be allowed to furnish a return for a tax period if the return for any of the previous tax periods has not been furnished by him.

@ Mr Sivaraman A R,

No... GSTR 3B return can't be file october-19 return without filing of September 19 return

NO Sir you cannot file October GSTR-3B without filing September month's GSTR-3B.

According to the Provision of Section 39(10 of the CGST Act 2017 :

"A Registered Person shall not be allowed to furnish a return for a tax period if the return for any of the previous tax periods has not been furnished by him."

Warm Regards.