The participants of ISC are selected through Sudoku Mahabharat. The Sudoku Mahabharat for this year is already over and the participants have been selected. So, one cannot participate if not selected.
But this is not a dead end. Just keep track of the website and particiapte in the regular competitions held here. Till the time the next competition begins you may download and enjoy previous competition sudokus http://logicmastersindia.com/lmitests/downloads.asp