In order to leave a Private Group from an Android device, follow these steps:
1. From the private group map, tap the menu icon in the top right of the screen.
2. This will take you to the Group Details screen. Tap on the menu icon and choose Edit Group.
3. From this next page, you can choose to LEAVE GROUP upon which you will be prompted to accept the the choice (LEAVE GROUP).
4. Finally, you will be taken back to the group map where you will be notified that you have left the group. Other members of the group will also receive a notification that you have left.