Srijit, if you look at the IISER Aptitude syllabus, it is based on your 12th subjects. You can check the complete syllabus at the official website: http://www.iiseradmission.in/index.php/pages/syllabus . Now we do not have any Coaching for IISER per se  but we do have coaching for JEE Mains and NEET. The syllabus is the same for these 3 subjects. But the exam pattern, marking and weightage vary. The preparation also remains the same. So if it interests you, you can check the relevant knockout packages between JEE Mains and NEET: https://learn.careers360.com/knockout-neet-may/ and https://learn.careers360.com/knockout-jee-main-april/ . Because we cannot authenticate 3rd party websites for you, this is the best we can help you with.