wrongly availed IGST instead of CGST and SGST

in FY 2017-18
in one of my client I have claimed IGST instead of CGST and SGST in GSTR 3B

in GSTR 9 total of. 2A and BOOKS credit matched but head wise there is a difference amount hence overall difference nullify effect

then how to do reversal of credit in IGST and how to take credit in CGST and SGST
please provide answer as soon as possible


Thanks in Advance