Summarize:

If you haven't already disabled Bixby Voice, you'll need to do that before you can continue. It's under the volume key on the left side of the Galaxy. It's near the top-right corner of the screen. A new switch will appear at the top of the screen. Now that you've disabled this button, pressing it will no longer open Bixby. The final step to removing Bixby is to disable it on the home screen.
Disable Bixby Voice. Press the Bixby button. Tap the gear. Slide the "Bixby key" switch to Off .