By default, the Ribbon icon gallery will display FontAwesome icons. But it is also possible to display one of the other libraries:
1. Select the icon library in the properties.
2. Hold the SHIFT key while clicking 'OK'.
3. Restart the application.
You can also update the registry key manually: HKEY_CURRENT_USER\Software\Pablo Software Solutions\WYSIWYG Web Builder 16\Defaults\IconFont