i lost the mail app on iPad after 12.0.1

Hi getanswersfor12,

Welcome to the Apple Community.

Apple's support article"

"Remove built-in Apple apps from the Home screen on your iOS 10 device"

Says:

"Restore a built-in app that you removed

1. 1. On your iOS 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."

Complete article: https://support.apple.com/en-au/HT204221

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The article: "Change the iPad settings"

Says:

Set up mail, contacts, and calendar accounts

1. 1. Go to Settings  > Passwords & Accounts > Add Account.
   2. To add a mail account, tap an email service—for example, Google, Yahoo, or Aol.com—then enter your email account information.

Complete article: https://support.apple.com/en-au/guide/ipad/ipad79520415/12.0/ios/12.0

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And, Iif you wish:

How to move and organize apps on iPad

https://support.apple.com/en-au/guide/ipad/ipad997db08a/ios

For more info:

User Guide for iPad iiOS 12

https://support.apple.com/en-au/guide/ipad/welcome/12.0/ios

Hope this works for you :-)