To see the record of all recent changes made to the questionnaire, click on the History button located on the top right of the page. This page will list the question that was changed along with the username of the person who made the change, and the time stamp for when the change occurred.
Starting with version 5.15 (Released December 12, 2016), users can now undo changes that they have made to a questionnaire. To undo changes in Designer, users can click on the Revert to this version button on the right to change the questionnaire back to that earlier version. For questionnaires edits made after the release of version 5.15, all changes to a questionnaire can be undone.