Diagnosis
You need to perform a factory reset. This erases all configuration and removes the eero from your account.
How to Fix It
Find the reset button on the bottom of the eero unit. It's a small pinhole. Use a paperclip or SIM eject tool. Press and hold the button. The light will flash yellow. Keep holding until the light flashes red. This takes about 7 seconds. Release the button immediately when you see red. The unit will reboot with a solid white light, indicating it is ready for new setup.
If That Didn't Work
If the light never flashed red, the unit may have been unplugged during the process. Ensure it is powered on. Press and hold the reset button for a full 15 seconds. Release. Wait 5 minutes for the full reset cycle to complete.
Heads Up
A factory reset does not automatically remove the eero from your app account. You must also open your eero app, go to the device in Settings, and tap 'Remove' to delete it from your account list. Do both steps.