I was preparing for engineering till now but have concluded that it is not my interest and now want to study at IIM. What should I do?

If you are in class 12th, the best option for you is integrated management program at IIM – Indore, which is a 5 years degree course equivalent to an MBA. Else, you can do 3 years any graduation preferably BMS, economic honors, BBA, etc. and you can prepare for CAT exam.