Your undergraduate school needs to submit curricula to IHMM for review and approval to become a part of the IHMM ST/CHMM student certification program. These curricula are generally in the area of environmental studies, environmental engineering, chemistry, biology, or geology.
Once your school has established with IHMM that it has a fully-accredited curriculum in the areas of study most likely to lead to a student, with experience in the field, being able to qualify for testing and certification for the fully-accredited CHMM certification later on, then IHMM enrolls the school and the school works with IHMM to communicate with students about the availability of the IHMM ST/CHMM program.