Cosomology is mainly a theoretical field interested in the Evolution of the universe and creation of Universe itself. Now Cosmology is a field which is a branch of Mathematics and Theoretical Physics. So if you want to be a Cosmologist then you need to either go for A BSc in Physics or BSc in Mathematics followed by a MSc in Physics or MSc in Applied Mathematics. After completion of MSc you can take admission in the PhD program at TIFR, IUCAA, ICTS or any other central university/state university and can do research in Cosmology. After completion of your PhD in cosmology you will become a Cosmologist and can join various research institutes/universities/colleges as professors/scientist or Researcher.

For more information regarding Career in Physics consider the link provided below:

https://www.careers360.com/courses/physics-course

For more information regarding Career in Mathematics consider the link provided below:

https://www.careers360.com/courses/mathematics-course

I hope this helps. Wish you a great day!