first lets make it clear that this works with android 6.0...
Step 1:-
First of all download google(version 6.14.24.21.arm64) apk from the link below:-http://www.apkmirror.com/apk/google-inc/google-search/google-search-6-14-24-release/google-app-6-14-24-21-arm64-android-apk-download/



And then install it on your device........

Step 2:-
After installing it go to play stote and search for google app and you will see that a update is available for it.so go ahead and install the update....



Step 3:-
Now open settings=>installed apps=>google app.


Now after you open that you will find an option called Manage Space.open it and click on=>clear all data...


Step 4:-
And now open settings and search for language & input option and open it..

In that open language and change it to English(United States)...


Now come to home screen and close all apps and long press home button you will get ur google assistant.

So go ahead and complete this process and start rocking with ur new assistant.any doubts and queries please mention it in the comments section below.