Appearance >> Customize >> Widgets – Panel

This is notice of Widget Panel

Here are the instructions about widgets. May you can get this notice on top of customizer. Your theme has _Number_ other widget areas, but this particular page doesn’t display them. 
You can navigate to other pages on your site while using the Customizer to view and edit the widgets displayed on those pages.

On Widget panel you can get this type of notice on top of the header. That’s why you need to understand on which  page have how many widget area are exist. So please go to template options you can get template structure there.

If you are trouble to add widget from customize you can go through Appearance >> Widget and drag specific widget to widget area. Otherwise here is the instructions.

Appearance >> Customize >> Widgets >> Widget area(May there other widget area name)– Section

• Click on Add a Widget
• Add One Widget
• Field form of the widget
• Click on Publish