In order to access Support Mode, Poké Ball Plus must be in standby mode (the LED is powered off) and not be currently connected to another device, such as Nintendo Switch or Pokémon GO Plus.
Support Mode is an option that allows you to access three different features on Poké Ball Plus:
Check the Remaining Battery Charge
Delete Pairing Information With Nintendo Switch
Delete All User Data
While in Support Mode, you can toggle between each feature by pressing the Top Button.
To exit Support Mode, press the control stick button once.