In order to complete a performance review assigned to another user, you must first have the appropriate user right. To find out how to assign this user right, please refer to the article How to give a user the right to complete a performance evaluation assigned to another user.
To select the evaluation to be completed, go to the Process Monitoring page. In the Process Monitoring section, click on the chevron to open the process in which the evaluation to be completed is located. Locate the employee you need to evaluate and click the To-Do button.
Within the modal, click on the yellow Complete the evaluation button. You'll be able to complete the evaluation, save it and submit it when you're done.