Unfortunately, Apple doesn’t provide an easy way to remove email addresses once they have been saved. Email addresses are saved automatically on your iOS device when you send an email.
If you have a jailbroken iPad, you can easily remove any unwanted email addresses using AutoFill Eraser. The app is free and it can be installed on any jailbroken device by searching Cydia for AutoFill Eraser.
Although the app is not optimized for the iPad, it works just fine in iPhone mode on the tablet. To remove an email address using AutoFill Eraser, you simply swipe on the unwanted email address and tap delete. You can also tap edit, then tap the red minus button and then delete it.