Hi there, bawl!
Thanks for stopping by the Apple Support Communities. We see you are having trouble getting the Fitness app installed on your iPad. We're happy to help!
In order to use the Fitness app on your iPad, you need to have an Apple Watch series 3 or later running watchOS 7.2 or later: Update your Apple Watch - Apple Support. Your iPad needs to be running iPadOS 14.3 or later: Update your iPhone, iPad, or iPod touch - Apple Support. You also must be using the same Apple ID on both the iPad and the Apple Watch: Sign in with your Apple ID - Apple Support.
Once you've confirmed the above configuration, restart all of your devices and try again:
Restart your iPad - Apple Support
Restart your iPhone - Apple Support
How to restart your Apple Watch - Apple Support
Should you still have trouble after that, please get in touch with Apple Support directly. You can do that here: Get Support.
Have a lovely day.