Even with the HomePod just being released it’s always good to know what to do if:
The HomePod isn’t responding after a restart
You want to reset HomePod to factory settings
You need to send HomePod in for service
You want to sell or giveaway your HomePod
Reseting the HomePod is easily done via the Home App however if your HomePod isn’t appearing in the Home app, there is another way to reset HomePod with the hardware itself. Here’s how to do that:
Unplug HomePod and plug it back in
Press and hold the top of HomePod, keeping your finger on top of the device at all times. If you lift your finger, you’ll have to start over.
After you press and hold on the top of HomePod, the spinning white light at the top of the device will turn red and Siri will tell you that your HomePod is about to reset.
Keep pressing the top of HomePod until you hear three beeps.
If this fails or resetting doesn’t fix your problems, your next step is taking the device to your local Apple Store.