I phone

did you remove it from your Home Screen?

From your Home Screen, swipe left until you get to the App Library.

Swipe downward and you'll get an alphabetical list of your apps.

Locate the app in the list or type the app name into the search field

Once you've located the app, tap/hold then drag and it'll pop out to your Home Screen

Organize the Home Screen and App Library on your iPhone - Apple Support

Naiscoot Said:

"I phone: I lost the mail app and how do I retrieve it"

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Reset the Home Screen Layout...

You'll have to re-download the apps. So, take a note of what is on each screen.

Go Here: Move and organize apps on iPhone - Apple Support

Scroll to: Reset the Home Screen and Apps to their Original Layout

1. Go to: Settings
2. Tap: General
3. Tap: Reset
4. Tap: Reset Home Screen Layout

no problem, glad to be of help!