You will find the corresponding option inside:
Dashboard >> Appearance >> Customize >> BuddyPress Nouveau >> Group Navigation.
Here you will get the following options to customize the navigation menu for groups. You can see your changes by navigating to a group in the live preview window.
- Display the group navigation vertically.
- Use tab styling for primary navigation.
- Use tab styling for the secondary navigation.
- Use tab styling for the group creation process.
NOTE: Customizing the Groups navigation order needs you to create at least one group first.