How to restore health app on iPhone 7?

The Health App has never been a delete-able App. No way for you to have deleted it. Maybe moved it to another home screen, or into a folder, but it cannot be deleted.

Use the Spotlight search by swiping down from the middle of the screen, when on the home screen, and try to find it. If its in a folder, it will tell you which one.

Here are the instructions for restoring a pre-installed app:

Delete built-in Apple apps on your iOS 12 or later device or Apple Watch - Apple Support

However, the Health app is not on that you can remove. Have you tried searching for it using Spotlight?

Use Search on your iPhone, iPad, or iPod touch - Apple Support

You should also check to see if you have restricted it.

Use parental controls on your child's iPhone, iPad, and iPod touch - Apple Support

Use Screen Time on your iPhone, iPad, or iPod touch - Apple Support