Make sure the Phantom you want to reset is plugged into power.
Hold down the back button of your Phantom Premier or Phantom Reactor for 10 seconds
Your Phantom will go in Stand By mode, keep pressing the back button of your Phantom un till you hear the Boot sound (release the button when you hear this sound.
Follow these instructions for all Phantoms in your environment.

Note* On Phantom II or (Reactor) when the device is in factory reset, the led light will blink in purple.

Note* All sounds for this firmware versions (DOS 2) are available here. It can help you to understand what is the current status of your product.

Open Devialet App on your mobile or tablet, and go into the top wheel of the Welcome screen and then select "add a new product"
Follow instructions to complete the setup.