Advanced sharing is an option available for the dashboard editors, who can manage access at the viewer, editor, and group levels.
To choose the advanced sharing option, click on the ‘share' icon
Viewers Tab
Here you can find all users (apart from editors) who have access to view a dashboard and the groups they belong to. Using the '+' icon
Editors Tab
Here you can see who are the dashboard editors and add them using “+' icon
Groups Tab
This tab is for managing group access to the dashboard. Here you can add groups using the '+” icon
All users with viewing access have a group membership. If no other group is defined, they belong to the default group. You can’t change the group for the user here - it can be done on the Viewers Tab.