Hello Akarsh Agrawal. Thanks for contacting Careers360 and we hope we will be able to answer your query.

I am afraid to say that you cannot change your exam mode to Online mode now. In fact, I should say that this mode should have been defined first itself. This is because most of the exams that bring in both online and offline modes for the students always specify first itself that this mode cannot be changed afterwards. 

Hope this helps you and all the best!