Courses that you have already enrolled using UTokyo Academic Affairs System (UTAS) will be automatically registered on the ITC-LMS. However, the actual course registration period with the ITC-LMS only starts one month before the start of classes.
Foe example, registration for courses offered in the S1 term (or S semester) will start around the beginning of March.
Please check here for details on the period for course registration for enrollees.