If shaking your iPad doesn't bring up the Undo prompt, Shake to Undo is probably turned off. You can turn it on in the Settings app under Accessibility > Touch > Shake to Undo.
How to turn on Shake to Undo
- Open the Settings app on your iPad.
- Tap Accessibility, then Touch. You can also type Shake to Undo into the search field at the top of Settings.
- Turn on Shake to Undo.
This comes in handy when installing your signature on an iPad. If iOS strips your formatting after you paste the signature, shake the iPad right away and tap Undo to restore it. See how to add your signature to Apple Mail on iPhone and iPad.
No room to shake? Swipe left with three fingers, or tap the undo arrow in the shortcut bar above the keyboard.