How do I message students who have not signed up for a self sign-up group?
If you have created a self sign-up group within your course, you can message students who have not yet signed up for a group and remind them to do so.
In Course Navigation, click the People link.
Open Group Set
Click the name of the group set.
Message All Unassigned Students
Verify that self sign-up is enabled for the group set  and that unassigned students exist for the group set .
Click the group set Options menu , then click the Message All Unassigned Students link .
Note: The Message all Unassigned Students link will not display if all students have been assigned to a group.
Canvas populates the recipient list with the names of students who have not yet joined a group . Type your message into the text area . Click the Send Message button .