I can’t design size chart anywhere

Hi! I am interested in purchasing your plugin so I am trying it out on a staging site.

I just installed the plugin’s free version, I activated it and I am creating my first size chart, but when I click “Add new size chart” it takes me to the WP Theme Customizer interface and it lets me select options about the size chart, but no design popup is displayed on the right side of the screen so I have no idea how my design is going or where can I populate the tables with information.