Setting off igst liability with sgst credit balance

We had a excess of VAT credit which was carried forward to GST. We got the ITC  for the carry forward in SGST electronic ledger. In July we had only interstate sales and no intrastate sales. During filing GSTR-3B  for July the credit available in SGST is not setting off the liability for IGST. In your earlier update you had mentioned that SGST balance credit can be used for IGST liability.

Kindly help and guide me with details process