Sideload the Pixel 3 launcher on your phone running Android 9 Pie
The Pixel 3 launcher has some changes compared to the older version (see image at the top of this article with the new Pixel 3 launcher on the right). For one thing, the pill found on the Pixel 3 launcher's app drawer once again contains the Google Assistant icon on the right side. The microphone icon was there for Android P Developer Preview 4, and disappeared in DP 5. Spacing of the rows in the launcher is a bit wider, and the way that users can choose to activate a split screen, pin the app, or get more info about it, has changed (see image at the bottom of this article).
Another thing you'll notice about the Pixel 3 launcher is that it uses adaptive icons on all apps for a more consistent look. And if you have a phone that is running Android 9 Pie, you can have that look on your handset too. All you need to do is sideload the updated Pixel Launcher from APK Mirror. The APK is signed by Google and the changelist mentions the Google Assistant button in the Google widget, larger buttons in the Recents' App Info tap menu, and forced adaptive icons for all apps.
The APK is "verified safe to install." You can find it by clicking on this link.