You can look up an individual student and add them to a cohort but the following method is more efficient if you have a bunch to do at once.
Manage Remote and In-Person Cohorts From the System Page
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Canvas Homework Submission: Student AnnotationCanvas Homework Submission: Student Annotation
Introduced in the Summer of 2021, the ability to submit a student annotation replaces the functionality of Kami.
Group Assignments in CanvasGroup Assignments in Canvas
You can create groups manually or you can allow them to be generated automatically during the process of creating an assignment.