You can upload a Brightspace group export. If your groups are not from Brightspace, use the following format:
Header 1,Header 2,Header 3[,Header 4 (optional)]
NetID,email,group name[,cluster name (optional)]
The following usernames could not be found in GitLab. They might be invalid or the user might have never logged in. If the username is valid, they will be added to their group once they log in once.