As I have completed my diploma in food technology so how to get admission or what is the process of getting admission in iit karaghpur for btech ?

Applications for IIT Kharagpur's B.Tech programme, which is based on JEE Advanced (after qualifying JEE Main), are only accepted from those who have completed or are studying for their 10+2 (or equivalent) with Physics, Chemistry, and Mathematics (PCM) as subjects.

Eligibility for B.Tech Admission

With only a diploma in food technology (without 10+2 PCM), you are NOT eligible for B.Tech admission at IIT Kharagpur or any other IIT via JEE Advanced.
If you wish to pursue B.Tech at IIT Kharagpur, you must complete 10+2 (or equivalent) with Physics, Chemistry, and Mathematics, qualify for JEE Main, and then JEE Advanced