i updated my iphone to ios 14.3 but my fitness app does not change to fitness ?

If you own an Apple Watch, Apple Fitness+ automatically appears as the center tab in the Fitness app on your iPhone. For iPad, the Fitness app is available for Apple Watch users to download from the App Store. The Fitness app is also available on Apple TV.

Note: Apple Fitness+ availability might vary by country or region. Learn what's available in your country or region.

I am unable to understand. What Apple watch do you have?

Know more here --> https://www.apple.com/apple-fitness-plus/

Did you also update your watchOS to 7.2?

I have same issue. I have xs max with 14.3 and Apple Watch series 5 with 7.2 The health app did not change.