Refund Eligible or not

Sir,

I am register in Gujarat .I had done sales in FY 19-20 in state of Maharashtra. In FY 20-21 I have issue credit note against FY 19-20 bill.

In FY 20-21 there is Less sales of IGST.  when I show Credit not is GSTR -3B  portal not accept negative value.

can I claim refund for the extra TAX paid ?  if yes than under which section its eligible?

How to solve this transaction because  in GSTR -3B portal not accept negative figure.

kindly Guide