iPhone app to replace lost Apple TV Remote

You’re right it’s not in the App Store but it’s on your phone in Control Center.

If you have an older Apple TV, you would need the remote to set it up though.

Set up the Apple TV Remote on your iPhone, iPad, or iPod touch - Apple Support

The latest iOS software has the remote control builtin.

Scroll down the qui k options list from the top right of your iPhone screen, yo will see Airplay, Flahslight and many things, in the bottom row i the remote.

To use remote successfully, your iPhone and your Apple TV must be hooked to the same Wifi.