When Commissioner of CGST feels that the order passed is not legal and proper, whether he can revise the order himself?.

No. The Commissioner of CGST cannot revise the order.
In the model law, for CGST and SGST, there are different
provisions in this regard. For CGST, as per Section 79(2), the
Commissioner of CGST if he finds an order or decision (passed
by an adjudicating authority) to be not legal or proper, can
pass an order setting out the points for determination where
he is of the view that the order is not legal and proper and
directing a GSTofficer sub-ordinate to him to file an application
to First Appellate Authority (FAA). Such application is then
treated by the FAA as if it were an appeal.