What rank should i get in JEE Advance to get into IISER

Hii Govind!
Although you haven't mentioned the category to which you belong in order to know the exact cutoff ranks, let me tell you that you need to get a rank within 10,000 to be able to get a seat in IISER for general category. The link given below will give you more details -
https://www.google.com/amp/s/engineering.careers360.com/articles/iiser-merit-list-and-cutoff
Hope this helps.
Good luck!