inter state sale return

Please reply I am registered dealer dealing sale and resale of electronic goods my most of the sale is made through amazon interstate sales to unregistered dealer. I want know the faite of goods return from some of the unregistered dealers. on the sale made to them i have already paid gst over it in the previous 3b returns . how the same can be adjusted in my pending gst returns.
I have already filed my gstr-3b return oct-dec nd already paid tax
Nd how we show sale return in gstr-1 oct -dec in case there is no credit debit note detail on those sale return
My most supplies interstate unregistered dealers