When students manage the groups, the planner cannot make any changes to the groups. To enable changes after the test is completed, do the following:

Open for resubmission for the group - this allows students to join and leave the group as if the test was still open (but it also gives them full access to the test again).
Once the student has joined the correct group, close for resubmission. Choose Deliver current when asked, and all candidates in the group will now have status Submitted.

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