Where to define the tooltip?

Hello,

You can add tooltip via Custom Attributes. Please go to Advanced tab, click "+ Attribute" button under Custom Attributes and add key = 'tooltip', value = tooltip text. If you want to use a custom icon for tooltip, add 3 attributes:

1. Key: tooltip.icon, value: dashicon icon or URL of the icon. See list of dashicons here https://developer.wordpress.org/resource/dashicons/
2. Key: tooltip.content, value: the content of the tooltip
3. Key: tooltip.position, value: left|right|top|bottom (one of them) to specify the position of the tooltip. It's optional.

Please try it and let me know if you need any help further.