Hi,
No  you cannot study mtech cyber security after pursuing btech from IT .
MTech Cyber Security is a 2-year duration post-graduate course that offers an advanced study on Cybersecurity methodologies and their applications in real-time scenarios.
Eligibility criteria -. Candidates seeking admission to the M.Tech Cyber Security course need to complete their B.E or B.Tech in Cyber Security or any other equivalent examination from any recognized university.
They need to secure at least 50% aggregate marks at the undergraduate level.

Hope it helps ..