If you have ever been typing information in the Rich Content Editor and accidentally deleted something or you made a mistake you wish you could undo, simply click CTRL-Z while in the Rich Content Editor and it will undo the last action you completed. You can also do this by clicking on ALT-F9, then clicking on the Edit drop-down list, and selecting "Undo".
Also, if you have accidentally deleted an Assignment, Discussion, Module, File, etc. within the Canvas course, you may be able to recover it.
1. Click on the Home button of your course .
2. Type /undelete at the end of the course URL in the address bar  and click the Enter button on your keyboard.
Undelete [View Image]
3. Click the Restore button next to any item you wish to restore to the course.
Restore Deleted Items [View Image]