How to get 'Google Assistant' on the BlackBerry DTEK50
The video below worked for me personally, it took a while to join the program, but it did.
Suggest hitting the "I'M IN" and then "JOIN"(as shown in the video) and then just leave it in the background - for so long that I forgot about it and cleared the running app in 2 hours time, when I went back to the Google Play Services playstore app - Volah, I was part of the program
https://www.youtube.com/watch?v=pSP6gICNfLY
Tricks:
https://www.youtube.com/watch?v=KVJcz3bR4Yo