Log in to your PeopleMatter account and go to the PERFORM module. Go to the drop down menu to the right and pick Admin Tools>General>Setup>People. Click Edit next to the Team Member's name, then the Evaluations tab.
All evaluations will be listed there. Click on the word Reopen on the row of the desired form. You will be prompted to verify that you want to make the form Incomplete. Then the form will reappear on the rater's Evaluations Due screen.