In Admission to IISER their eligibility criteria is through Jee Advance is

JEE Channel: Candidates in General category securing a rank within 10000 in the Common Rank List (CRL) of JEE Advanced 2018 are eligible to apply. For candidates belonging to reserved category (OBCNC, SC, ST, PD), their category rank should be within 10000.

You have to apply online for it!

Hello ,

this is to inform you that this rank will give you a seat in the pretigious institutions of our country IIT but not assure you the group.also you will not get a seat in the IISER.all the very best for your future.