Hi Gitanshi

You can pursue Marine engineering after completing your undergraduate level of Mechanical Engineering in B.E/B.Tech Mechanical Engineering or Diploma in Mechanical Engineering. 

I'll suggest you a few courses for marine engineering:

1. GME course

GME stands for Graduate Marine Engineering. GME course after mechanical engineering would give you the licence to enter merchant Navy. 

The duration of this course is 1 year.

Eligibility criteria: minimum 50% in English language at 10th or 12th or in degree exam.

You should not be more than 28 years old.

And most importantly, you should satisfy all the health requirements that are necessary to join Merchant Navy.

I'll suggest you some institutes offering GMU courses:

Academy of Maritime Education and training, Chennai

Garden reach ship builders and engineers Ltd, Kolkata

international Maritime Institute Ltd, Greater Noida

Samudra institute of Maritime Studies, Lonavala, Maharashtra

Vel's Academy of Maritime Education and Training, Chennai

Also there is IMU ( Indian Maritime University) , it has no. Of training location all over India. It also puts up notifications for same.

2. You can also do M.E/M.Tech Marine engineering .

Time duration is 2 years

 3. There are Diploma courses as well.

Marine Engineering is basically discipline of applying engineering sciences to Develop , Design, operate and maintain on-board systems maintenance, so it includes your Mechanical, Chemical, electronic engineering and computer science. 

You can also get extra information from DG shipping website.

All The Best!!