If you have those devices and didn't get the google assistant yet, here's how to enable it.
If your device is rooted, simply add " ro.opa.eligible_device=true " to your build.prop located at /system and you can skip step 5 and 6.
If your device is not rooted or you don't know what rooted means simply follow all the steps:
The first thing you need to do is to set your default language to English (US). To do that go to Settings -> Language and Input -> Set English (US) as default.
1. Go to https://play.google.com/apps/testing/... and register for the beta program for the Google app.
2. Go to https://play.google.com/apps/testing/com.google.android.gms and register for beta test program for Google Play Services app.
After registering you will get an update for both of these apps in few minutes.
3. Go to https://play.google.com/store/apps/details?id=com.google.android.googlequicksearchbox&hl=en to update google app.
4. Go to https://play.google.com/store/apps/details?id=com.google.android.gms&hl=en to update Google Play Services.
5. After that install fake gps and set your location to somewhere in the US.
6. Install a VPN service like Tunnel bear and set your VPN to use US servers.
7. Go to settings ↪ Apps ↪ Google . Clear Data of the app
8. Go to settings ↪ Apps ↪ Google . Clear Data of the app
Restart your device. After the device restarts hold your home button to get greeted by the all new google assistant.