You may find that you are unable to set a custom launcher as default on your Android Nougat despite tapping set as default. I'll show you how to fix this quickly:
How to change default Launcher on Nougat
Install the custom launcher
Go to Settings on your phone
Tap Apps
While on the Apps screen, tap the Gear icon (App settings) at the top
On the next screen, tap Home App
You can select the launcher of your choice there and it'll be set as default