@ SimranSahi
In my opinion, I would not advice you to change your course, as this would make you appear desperate. You should have your career path well thought out; changing your course would only make the visa officer feel you really do not know what you want. I would suggest you write a detailed explanation in your SOP as to why you have decided to study a course unrelated to your previous studies, and the potential benefits you stand to gain from studying your proposed course. On the flip side you can decide to appeal for an administrative review, but that would surely take time.
Good luck.