Where is the Health App? Can't find it.

Usual reason is the use of screen time / parental controls, or the use of Focus, or this is a managed iPhone with profiles loaded. Or you’re on a really old iOS version.

The Health app cannot be deleted, though it can be hidden away:

Delete built-in Apple apps from the Home Screen on your iOS 14 or later or iPadOS device or Apple Watch - Apple Support

Swipe to the left repeatedly until you’re on the last page of the iPhone display and now viewing the app library, and enter Health in the search to look for the Health app there.

Did you check the App Library to see if it got moved there? If it didn't and it isn't on any of your iPhone's screens, it may have accidently been deleted. You can always redownload it from the Apple App Store in that case.