start with a refreshing beverage of your choice and sit with a pen and paper, analyse the time left and main topics that carry most weightage, start with the topics you find interesting/easiest. keep crossing them off you lost as you move ahead. you will get through them👍💯
Look if studied whole about that particular subject then I think you should not worry too much just relax your mind and revise things !!! and if you haven't studied till today about that particular subject then I think you should just let it go because you are not going to rock that exam in only 3 days !