E mail
How can I change my I cloud email address as my other email user name
iPad Pro Wi-Fi + Cellular
See the following: Change your Apple ID - Apple Support
and be sure to do the following as instructed in that link:
Before you change your Apple ID email address, you need to sign out of every Apple service and device that uses your Apple ID. If you want to use your iPhone, iPad, or iPod touch to change your Apple ID, stay signed in to your Apple ID on just that device.