Self-evaluation means that the student will not only give feedback to their peers, but they will also be asked to give themselves feedback. If students have to evaluate 3 hand-ins then their 4th evaluation will be their own piece of work. Students self-evaluate with the same rubric used to evaluate their peers and always complete the self-evaluation after giving feedback to their peers.
After you've created an assignment, go to the assignment settings page and click Feedback on the side menu. Select the option to Require students to evaluate their own submission (self-evaluation).