How can I operate the 6-36875 annoucement with an old zw transformer? What app will work?
Welcome to the forum.
To operate the announcement in your car with your present ZW, you need a Lionel 6-5906 whistle/bell activation controller wired in series with the track connection to make it a bell controller.
http://www.lioneltransformer.com/lionel_6-5906_lionel_sound_activation_button_brand_newYour second option would be to upgrade your transformer to a newer one that has both the whistle and bell buttons included in its design.
Larry