Gstr 3b negative values

Sir,

Q1.We have raised Credit Notes in 0% Tax category(Pharma Expiry Goods received) where do we fill the values in GSTR 3B. The Sales Value after deducting the Credit Note value goes in Negative( Sales Value is less and Credit Note Value is High). 

Q2.Is it Correct that we raise 0% Tax credit note for Expiry Goods in GST.