As per the official to apply for M.tech QROR in ISI Kolkata, You should have completed BE, B.tech or other qualification Master’s Degree in Statistics with Physics and Chemistry at the (10+2) level or Master’s Degree in Mathematics with Statistics as a subject at undergraduate or post-graduate level, and Physics and Chemistry at the (10+2) level.

The programme is offered in two streams:
• Statistics Stream:  For candidates with qualifications Master Degree in Statistics or Master’s Degree in Mathematics with Statistics as a subject at undergraduate or post-graduate level.
•Engineering  Stream: For  candidates  with  an  undergraduate  degree  in  Engineering or Technology (B.E, B.tech) or any other qualification considered equivalent (such as AMIE).

The selection procedure: All  candidates,  including  sponsored  ones,  are  admitted  through written tests and interview. For this programme admission a valid GATE score is not required. You can check the complete information with given link.

https://www.isical.ac.in/~admission/Documents/Eligibility-and-Selection-Procedure-2018.pdf

Good Luck!