Question

You can undo up to the most recent 40 actions by clicking the undo button.

Answer 1

The answer is true. The Undo command is set up on the toolbar.  You can undo up to 40 edits in your plan by clicking on the Undo button.  If you want to undo all of the revises made, simply quit (close your Internet browser window or start a new plan) without saving.