Cross set-off of CGST credit with SGST cannot be done.
CGST Credit can be first utilized for payment of CGST Liability and balance, if any remaining in the CGST Ledger will be used to clear your IGST liability.
Refer SECTION 49(5) of CGST Act 2017 for manner of utilization of CGST, SGST, IGST and UTGST credit.