RCM paid by IOCL on transport contract

Can be reported in table 3.1 (a) GSTR 3B , without putting any tax in corresponding tax column . (As it's taxable supply , & only the liability to pay is shifted on Receptient)

And in GSTR 1 need to be reported in table 4 by clicking the option RCM Applicable therein.

Note : In 3B it can be also reported under 3.1 ( c) , but it's better to report in above said table