How do I prevent students from switching groups in self sign-up groups?
When self-sign up is enabled for a group, students are able to switch groups. To prevent students from switching groups you can disable self sign-up at any time.
If a group has a student leader, the leader will be able to manage group memberships through the course People page regardless of self sign-up settings. However, student group leaders cannot change the number of members allowed in a group.
Open People

Open Group Set
Click the name of the group set.
Edit Group Set
Click the group set Options menu [1], then click the Edit link [2].
Save Group Set

Deselect the Allow self sign-up checkbox [1]. Click the Save button [2].
[Content retrieved from https://community.canvaslms.com/t5/Instructor-Guide/How-do-I-prevent-students-from-switching-groups-in-self-sign-up/ta-p/689]

