Hello

There is no link or connection between these two streams.if you are willing to work in computer science field, you can work. It's totally upto you. Their is no problem to move in for computer science.

You have to work extra hard for computer science as you completed BTech from mechanical. Otherwise their is no problem.

Usually, it is possible in most Universities abroad, however you need a strong profile relevant to Computer Science, Experience and Projects. I would advise you to specialise in Software, Machine Learning, Analytics and relevant fields, besides keeping up with your Coursework in Mechanical at your University. Try securing good Internships, especially Research Internships and Projects in domains of Computer Science. Post which you may pursue a short 2-4 year but strong work experience in the IT/Service/Software Industry in India. I believe your Profile will be ready for applying to some of the best Universities across World for MS in Computer Science.