Step 1: Make sure the Google Play Services on your devices is updated to version 10.2.98 or later. If not, either download the latest version from here, or wait for your device to update it automatically.
Step 2: Change your device's language to English (US). To do so, navigate to Device Settings > Language & Input > Change it to English (US).
Step 3: Now make sure your Google App is updated to the latest version. If not, just go to Google Play Store and update the Google App. My device was running version 22.214.171.124 at the time of writing this story.
Step 4: Clear cache from your Google App data. This is will clear all the previous settings on your Google App. Also, make sure your Google App language is set to English (US)
Step 5: Once done, just tap and hold the Home Button of your device and you will see a message pop from the bottom asking you get started with 'Google Assistant'. Enjoy!