I can’t find my fitness app on my iPad

You need more that just the app.

Your iPad needs to be updated to the latest iPadOS 14.3

You need a compatible Apple Watch ( series 3 or later ) updated to its latest WatchOS version and, also, Bluetooth connected to your iPad before the iOS App Store will let you download/install the Apple Fitness+ app.

You need to have or purchase an Apple Watch series 3, or later.

No options.

Once you’re upgraded to current, have an Apple Watch associated with the Apple ID, and have a Fitness+ subscription, reboot your iPad, and you’ll probably then be able to find and download the Fitness app in the app store. The reboot was what solved this where-is-fitness problem with an iPad here.