As recommendation you can save your work from time to time, just hit Ctrl + S this will save a version of your work that you can go back or restore later.
Also pressing Ctrl + Z will undo previous actions.
But if you want to restore the original version of your template or go back in time to a previous version, just:
- Go to the settings of your page.
- Under Backups pick a version you want to restore.
Please note that restoring a previous version will delete your current work.