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.
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 .