Hey there

Iits and IISC do not accept JEE mains marks for admission into these colleges. Rather JEE mains marks are only a criterion which one should pass to sit in JEE advanced which decides whether you will be selected or rejected. Iits take admission through JEE advanced and IISC take through kvpy and jee at UG level. For masters you can give gate to get into these colleges.

Check about JEE mains

https://www.google.com/url?sa=t&source=web&rct=j&url=https://engineering.careers360.com/exams/jee-main&ved=2ahUKEwjXyM2F-9DkAhWkguYKHa6XB9QQFjAAegQIARAB&usg=AOvVaw1k3rMyr-Osb0qy4gsPfOaR good luck