Hey Alok, 

Sorry but there is nothing thst can be done for to get admission in any IISER for the masters course. They are currently providing only integrated BS MS courses in various disciplines and Doctorate programmes but individual MSc programs are not available.

You can check the information using the official website. 

https://www.iiserbpr.ac.in/index.php?category=doaa&pid=course-content

But still you can go for JAM examination for pursuing MSc from various IITs, NITs and IISc.

Here is the link for your reference. 

https://university.careers360.com/articles/jam-eligibility-criteria/amp

Hope it helped you..