With a small layout put one train on the tracks, enter it’s address, and stop it before putting the next train on. When you have that train on the tracks set it to a very slow speed, then re-select the first train and set it to a slow speed. Yes, this is awkward with the Zephyr because of all the button pushing to select the locomotive you are currently commanding. The Zephyr lacks a “last” button like TV remotes, which some competing products have.

I have never read the source that says the display will read “GOOD”, but that is not my experience with the Zephyr. Usually you write the value to the CV, then read the CV and make sure you get back what you wrote.