Surplus in GST -3B

In the month of September 2019, we have outward supply of IGST Rs - 13,500.00-/- but the same month we have credit note value of Rs - 30,289.50/-  now we having surplus of Rs 16,789.50-/-  When I'm going to file monthly GST 3B will not be accept negative value, hence in the case where I need to file the credit note value in GST 3B.