Hello Suraj,

Cosmologists are people that have an inherent interest in knowing about the universe's origin and studying the celestial bodies.

The basic requirement is to get a Bachelor's degree in Physics, astronomy, astrophysics, mathematics or engineering with a relevant subject like aerospace engineering. 

This degree can get you like a Research Assistant job in cosmology.

You can pursue Master's or doctoral degree in Physics, Astrophysics, Astronomy, Aerospace engineering or Mathematics so that you can do research yourself or become a cosmology professor in a university.

Hope this helps.