If you are interested in pursuing MBBS the first thing to do is opt for PCB in class 11th and 12th / Intermediate . Since you have just completed class 10 it doesnt matter if you had studied in a school coaching for IIT. Also in class 10 you have all subjects, so opting for Physics, Chemistry and Biology is the next step. As you say your school is coaching for IIT, you must already have been giving more weightage for Physics and Chemistry, you just need to add Biology too. 

For admission to any medical college in India, you have to appear for NEET. Preparing from NCERT textbooks is highly advisable as NEET is conducted by CBSE.

Note: Only AIIMS and JIPMER have their own entrance test for admission. Rest all are based on NEET. 

Please go through How to study Medicine after class 12