I am a Science student. How can I get admission for B.A History?

First of all if you have interest in history so you will persue  graduation  in this subject 

It is common when you will fill the college form where they ask that which subject or stream you wanna choose . So where you should choose B.A stream and history as subject.

Thnk you . 

If you want to do B.A. History, you have to clear CUET. After that you can study B.A. History from Delhi University. It doesn't depends on your stream.