We would like to inform you the Google assistant update will be rolling out via Google, so your phone with Marshmallow and Nougat OS should get it automatically. This is a server-side update, so your phone should automatically receive the update via Google play services. We also request you to once change the system language to English (US). To check if you have Google Assistant or not, just long-press your home button. We appreciate your loyalty, thanks for sharing your concerns with the Community!