Systeme io Questions and Answers (FAQ)
Once the domain (or subdomain) is changed, Systeme io will automatically send an email to all existing students who have enrolled in the course to notify them about the changes that take place.
The students will be given a new URL so that they can log in and access their course.
So that point onward, students need to use the new link given as the old one will no longer be workable.
There are other implications of changing the domain (or subdomain), read What happens if I change Systeme’s Subdomain.