Hello Deepak,
I am sorry to inform you that you can't do such thing. As MAT 2019 February, paper based exam is going to take place on 9th of Feb. So, it's totally not possible.
But if you are not confident for this attempt then you can apply for May 2019 attempt and you can choose paper based exam form. And next time before filling the form go through FAQ's properly and apply according to your prefrences.
I hope this helps you.
All the best !!