For those of you running non-Pixel/non-Nexus smartphones on Android 7.0 or 7.1 Nougat, you will need to grab the Google Assistant Velvet.APK file and install it manually on your /system/priv-app/Velvet directory.
This will allow you to get Google Assistant on non-Pixel/non-Nexus Android smartphones running custom ROM like CM14 or CM14.1. It will ONLY work on custom ROMs running Android 7.0/7.1 Nougat so make sure you have such a custom ROM installed.
You will also have to edit the build.prop file (use Build Prop Editor app free on Google Play Store) and add:
What is an APK File?
APK File is a file/app that can be installed on any Android smartphone or tablet. Using an APK file, you can install Android apps manually on your Android device.
You do not need a rooted Android device to install APK files. For installation instructions, please see below.
Then also clear your Google App storage and reboot!
This APK was pulled straight from a Google Pixel smartphone and is compatible with any Android device running Android 7.0/7.1 Nougat.
How to Install APK Files
You will need to make sure Unknown Sources is checked ON in Settings to install APK files. We do recommend you to use a file explorer app such as ES File Explorer, available on the Play Store for free, to install these apps.