As you want to get the details of process to join Merchant Navy after completing B.Tech in Computer Science so here is the information of the same for you:

Generally there are 2 possible ways to get into merchant navy for candidates belonging to science/engineering background.

You can either join merchant navy as an fifth engineer or you may join as deck cadet.

Most of the companies, for their merchant ship, like to recruit candidates who have done their engineering in civil, mechanical electrical or information technology however, to join as an deck cadet, qualifying +2 with physics, chemistry and maths is enough.

There is one more way that is of giving the exam of CDS which is conducted by UPSC every year