You can't... look at the OCWP duration. It won't exceed your study permit and as studies are over, you aren't studying full time. One of the condition to use OCWP is "to be a full time student", as you have completed your studies, you do not have any status at the moment. Yes you do have 90 days window to decide your next move if you wana further apply for study permit or PGWP.
But then ground reality is, people do work full time even after completion of the program (but it's illegal).