On Windows use ctrl-z to undo
In common with most other applications you can use ctrl-Z (Win) or Cmd-Z (Mac) to undo some actions. In most cases the undo feature will allow you to go back about 1-3 steps.
Undo does not work inside the text widget and in some other places. We are working to fix this but we can not estimate a date when this improvement will be released.
On a Mac, use cmd-z