GSTR1 Amendment

D.J. Marketing (33 Points)

03 January 2018  
For Goods Returned in Aug 17 I have issued A Credit Note to the party. Party has also raised Tax Invoice showing goods returned as sold to me.
GSTR1 till September 17 already filed. How to resolve this issue. Can Credit issued and already shown in Aug GSTR1 be cancelled and Tax Invoice entered as Purchase in Aug???