How to download apple remote for Apple TV 3rd gen

The Remote widget in Control Center works for Apple TV (3rd generation or later) with software 7.5 or later.

The Remote app from the App Store is no longer available.

You would use the remote in control centre, as per the support article you linked from. I will paste again for reference.

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

the remote app works for all appletv types