The new HTC One M9 isn't all that different on the outside from its predecessor, but it does offer some new software tricks. One of them is the capability to customize the order, and even add or subtract from, your device's navigation buttons.
The navigation buttons are the back, home, and recent apps' buttons sitting in the black bar at the bottom of your screen.
To edit your navigation buttons, launch the Settings app and select Personalize.
Next select Change navigation buttons.
A list of various options will be presented, with only the default three being selected. Again, those are Back, Home and Recent Apps. You can add one more to the navigation dock, and rearrange the icons to fit your personal preference.
The available options are: Turn off screen, Auto rotate, Hide navigation bar, Quick settings and Notifications.
My personal favorite out of the bunch is the Notifications option. With it enabled, instead of having to swipe down from the top of the screen I can tap on the button and the notification shade slides down automatically. It's not an earth-shattering feature, but one that's useful nonetheless.
Rearranging the icons is done by touching the three-lined icon next to each option and dragging it to its new home.
Any changes you make, be it adding or removing an option, will not be reflected in the navigation bar until you press Done at to bottom of the screen.