How I can do mtech during a govt job

Hi Abinash !

Yes brother you can continue your studies along with your job .

There are various Work Integrated Learning Programs offered by many institutions.

One of them which I know is BITS Pilani Work Integrated Learning Programmes (WILP)

BITS Pilani Work Integrated Learning Programmes (WILP) are technical continuing education programmes designed for employed professionals working in engineering and technology domains.
WILP also offers degree and certificate programmes under Corporate Partnerships to leading organizations from several industries customized to suit their Learning & Development requirements.

Duration: 2 years (four semesters)

Fees:
Application Fees (one time) INR 1,500
Admission Fees (one time)        INR 15,000
Semester Fees (per semester)    INR 40,750

You can also get your company to sponsor for your education.
So, Basically you will be working normally full time and studying in your free time.
The course lectures are online and you have to visit exam centres only to give end of sem exams.

But....

It is not possible to purse a full time degree in IIT/NIT by doing job in a core industry. Doing a part time course in IIT/NIT is not much valuable when compared to the full time degree in the same institutions.
If you cleared the exams and got admission in top colleges like IIT/NIT then I suggest you to leave your job and continue with your college degree. You can easily get job after completing your M.Tech in top institutes.