How do I find the Apple fitness app on my Apple tv

The Fitness app is available on the Apple TV set-top box (4th generation or later) with software tvOS 14.3 or later, in countries where this service is available.

The Fitness app is not available on third party devices with the Apple TV app.

Devices you can use with Apple Fitness+ - Apple Support

There is no Apple fitness app that I can discern.

There is the fitness app for women called Sweat. Was that what you were looking for?