In order to add a reviewer first we must go to the reviewing section by clicking reviewing on the top bar

This will take us to the Reviewing page. from here click on Reviewers.

That will take you to the Reviewers page which will list all of your reviewers (if you have any)

Here you can view and edit infomation about your reviewers. 

To add a reviewer click on Add Reviewer.

That will bring up a slide out menu.

Enter the infomation of the person you want to be a reviewer and then click add.

Your reviewer will then be added to the list. 

If your revewer has not signed up make sure they use the Email that you just used when they do otherwise they will not be registered as a reviewer.