Hey Manoj! 

The authorities will release the cutoff of jee mains 2019 for top iiit's in online mode and will use it as a screening process for admission.

The opening and closing ranks will be available in the jee main 2019 cutoff for top iiit's. Those candidates who meet the cut off of jee main 2019 for top iiit's will have more chances of admission into the institute and course of their preference. 

For more information you can look up her - 

https://engineering.careers360.com/articles/jee-main-cutoff-for-top-iiits

Wish you all the best!