Stock return

Company has returned the old stock to the seller in the month of oct (old stock as of 30.06.2017) and we are going to receive credit note, as payment for the stock is already done.

Now where to show this in gstr return. Where to show in gstr-3b(please specify column and how to fill) and also where to include in gstr-1 or gstr-2 ?

Also how this will effect the liability of our company ?

Please reply asap.