How To Remove Default Apps From Apple Watch. Go to the Apple Watchs home screen. FYI the Mail App on an iPhone can indeed be removed.

In that case its a good idea to let them know youre replying on your Apple Watch by adding the default Sent from my Apple Watch signature in the iOS Watch app My Watch tab - Mail. Tap the delete button on the app that you want to delete. WatchOS has allowed users to delete Apple Watch apps directly on the wearable but only for third-party software.
However you can hide specific apps to keep your Apple Watch Home screen organized.
On your iOS or iPadOS device touch and hold the app. One of the nice new options is you can now tidy up apps by removing even Apple. Tap the X on the app icon you want to remove. Open the Apple Watch app.

