Corrections in previous filings

Vignesh P (B.Com) (80 Points)

21 October 2017  
I have filed GSTR-3B for the month of September yesterday (on 20th Oct 2017). I was informed by the client that they have not taken into account a SALES Return.
The purchaser has reversed his input.
can anyone guide me on how to record this sales return transaction in the returns of the next month.

Thanks and regards
Vignesh P