If you wish to take admission in CSE then you have to appear for GATE CSE paper. Now it may seem to you a bit tough but let me assure you every year there are lot of student who does such transition and they do absolutely great in there career undoubtedly. Now the thing you should be keen about is that you are interested in coding and learning Mathematical concepts in CS which are quite different from the mathematical operation and tools used in ME. So you need to keep a open mind in terms of learning and with a good amount of hard work you will crack it and will find a successful career ahead.

To know more about GATE visit the link below:

https://engineering.careers360.com/exams/gate

To know more about CSE visit the link below:

https://www.careers360.com/courses/computer-science-engineering-course

I hope this answer helps. All the very best for your future endeavors!