Negative figure in GSTR-3B

In July 2025, we file GSTR-1 and GSTR-3B  return of export with payment of tax. But in August 2025 amand bill with payment to without payment of  tax. As result GSTR-1 show negative figure but GSTR-3B show zero figure and we filed return. As result of amand our taxable value less  and IGST paid more in August 2025. Now we want correct GSTR-3B as per GSTR-1. In September 2025 GSTR-3B, we increase taxable amount and reduce IGST and our IGST show Negative Figure. Please suggest correct treatment.