Theer is two step procedure to get admission in IITs for M.tech programme. You will have to apply to individual IITs through your respective portals and also register to Common Offer Acceptance Portal (COAP) to accept admission offers. There are many cutoff factors like number of candidates appearing in the GATE exam, number of applications for admission etc. Also, the cutoff is category-specific and course-specific. You can take an idea with the previous year cutoff of the particular course with the given below link.

https://engineering.careers360.com/articles/gate-cutoff-for-iit-dhanbad

Good Luck!