How do I enable Shake to Undo on my iPad?
If shaking your iPad doesn't bring up the undo prompt, Shake to Undo may be turned off.
Open the Settings app on your iPad.
Search for Shake to Undo.
Turn it on.
How to get shake to undo on iPad
Turn on Shake to Undo in iPad Settings if shaking your device to reformat a pasted signature isn't triggering the undo prompt.