https://www.youtube.com/watch?v=pmbL8ULZOP0

How To Remove Leanback Launcher from Your Nvidia shield TV On Oreo. #superusertechmods #nvidiashield #leanbacklauncher 
https://www.youtube.com/channel/UCSIk...
if you want to change your leanback launcher make sure you install a 3rd party launcher like nova launcher or sideload launcher first.
Then install fast boot drivers, enable developer options on your Nvidia shield tv, you can use nova launcher sideload launcher or thanks to Andrew Blower for telling me about sideload channel.
Irish Droid also for heads up, installing tv launcher could bring the launcher back again.
But for me it didn't so worth trying it out from the playstore
commands 
adb devices
adb shell 
when in shell type    pm uninstall -k --user 0 com.google.android.leanbacklauncher 
it should say successful
then type
pm uninstall -k --user 0 com.google.android.tvlauncher