How to customise Navigation buttons on HTC phone running Marshmallow

And Sense 7 I would like to add. Navigation buttons are simply the home and such buttons on the lower part of the screen.

You can’t remove the default ones, but you can add ONE more button.

Settings > Personalize > Change navigation buttons

Just move them around as you wish, or add a fourth button. Just tap DONE when you want to see your changes.