You must say the phrases 'Hey, Google' and 'OK, Google' twice each.
Tapping one of these notifications will begin the process of teaching Assistant your voice. Click the plus sign in the bottom right corner to begin multiuser setup. You can also get to the voice recognition setup by going to Devices > Settings > More > Shared Devices. You should find a notification there that also says Multi-user is now available. Tap the action overflow button in the top right corner of the card for your Google Home and select Settings.
If you don't see the notification, tap the devices button (an icon of a television and a speaker) in the top right corner. When you open the Google Home app, you should see a notification that says Multi-user is now available.
