where do I find the apple tv app

If you are running MacOS 10.14 (Mojave), the iTunes app is still there. The Apple TV app got introduced in MacOS 10.15 Catalina when iTunes was replaced with the TV, Music and Podcasts apps.

https://en.m.wikipedia.org/wiki/MacOS_Catalina

Macs need to be running MacOS Catalina

You’re welcome