Filed IT return under old scheme , can he file revised return under new scheme

No, not accepted by CPC.

Yes, he can file the revised return under the New Tax Regime — but only if he does NOT have income from business or profession.
A revised return under section 139(5) replaces the original return, and for non-business taxpayers, the option under section 115BAC can be exercised again while revising.
However, if the assessee has business/professional income, the regime cannot be changed in a revised return once chosen in the original return.