Apple Watch compass

First, he needs to download the Compass app on his iPhone from the Apple App Store.

• Open App Store on his iPhone
• Tap Search then type Compass
• Compass app by Apple.

Restore a built-in app that you deleted

1. On your iOS or iPadOS device, go to the App Store.
2. Search for the app. Make sure that you use the exact name of the app. Find the correct name of built-in apps.
3. Tap  to restore the app.
4. Wait for the app to restore, then open it from your Home screen.

If you have an Apple Watch, restoring an app to your iPhone also restores that app to your Apple Watch.

Is the Compass app also on his paired iPhone?

Which iPhone model ?

Read here => Delete built-in Apple apps on your iOS 12, iOS 13, or iPadOS device or Apple Watch - Apple Support

Please check and make sure the Compass app is on his iPhone.

See theCompass app icon in my previous post. Enlarge it to see the details.

You're welcome.