40G Certifier Changing a site label

How do you change the Label ID when using Simple Labels on the Viavi 40G Certifier? I see a field that says Next Label but nothing happens when I click on it. 

The Next Label field on the 40G Certifier Project Setting screen is a display only field. To change the Label id (Letter or Number) click on the Label Source field and then on Simple Labels. The unit will present you boxes to edit the letter and number fields. Be sure to hit the check mark icon to save your way out of the edit boxes and then label screen.