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.
When you are setting up an assignment, select 'allow students to evaluate their own hand in' under the Groups and peer grading heading.
If you've already created an assignment, go to the assignment page and select edit assignment.