First, be sure you eject the GO plus from the app in settings.
Next, shut the app and reopen it.
Now maintain down on the Pokémon GO Plus button for 5 seconds. Doing this can trigger the button to show blue.
Lastly, maintain it down from one other 5 seconds til it vibrates.
Congrats, you’ve manufacturing facility reset it! Now simply reconnect it in settings!
It labored for me, let me know if it really works for you!