Version history lets you undo changes to your SmartFlow, by restoring it to an earlier published version instead of rebuilding it from memory.
To restore a previous version open the SmartFlow in question and click the version history icon next to the Help center link in the top toolbar to open Version history:
Each previously published version is listed by date, with the most recent labeled "Last published changes."
Select a version and click Restore.
Restoring discards any unpublished changes currently in the editor, and this cannot be undone. If you want to keep your unpublished changes, publish them first so they become a restorable version themselves, or duplicate the SmartFlow before restoring.
The restored version is loaded into the editor as unpublished changes. You still need to publish it for the restored version to go live.
Restoring currently covers the form, setup, greeting screen, end screen and document. Changes to automations and email templates are not included and are not affected by restoring.