Unplug the power cable from your speaker. Wait for 10 seconds. Plug it back in, and wait until all 4 lights on the top illuminate.
Repeat step 1, 10 more times (so a total of 11 times).
After you plug your speaker back in the final time, you'll need to wait a few moments for the device to reset. It will announce 'Welcome to Google Home. To get started, download the Google Home app on a phone or tablet,' to let you know that it’s ready for setup.