Hello Yash,

Hope you are doing well.

In the IIT's paper, questions are based on the Application Of Concepts. You should have a clear understanding of the concepts of the previous Grade to grasp current Grade IIT stuff. Cracking IIT needs a lot of creativity for problem solving in Physics, Chemistry and Maths.

Some Books I will recommend:

1. IIT Foundation Physics Class 7 by Pearson
2. IIT Foundation Chemistry Class 7 by Pearson
3. IIT Foundation Maths Class 7 by Pearson
4. IIT Foundation Science Class 7 by S.Chand
5. IIT Foundation Maths Class 7 by S.Chand

Internet is the best way to understand and learn new concepts. You can browse for videos and notes on the topic you are having problems on.

IIT requires understanding of the concepts very well. You should also read books aimed specifically at a particular subject, like:

1. The Feynman Lectures Volume 1,2 and 3: These books are really treasure by the most famous physicist of all time, Feynman. These three volumes would make you grasp the concept very well.
2. AP Chemistry by Zumdhal: This books is really a good hunt for Chemistry with amazing explaination of concepts and intense questions for problem solving.

At last, I want to say that, don't pressure yourself and enjoy the process.

Good Luck!