First of all I notice that some people are getting it since yesterday, so if you wait for a few days then you might get it as well. If you don't want to wait then the way to do it is first set your language as English US, then sign up for Google App beta and Google play services beta. It is a simple enough task only make sure to use the account you are using on your phone. Once you do this then open play store and go to beta tab, you'll notice updates for Google app and google play services which you have to do. Once updated, restart the phone and then either long press the home key or go to Google app and setup the assistant.