Go to Administration > System Settings > SQL database backup
Click the down arrow in the “Select a file to restore” list and select the backup you want to restore from the drop down list. Next click the Restore database button. Once the restore has finished be sure to restart Mango to insure all your configuration is loaded properly.
If you are having issues starting Mango you can first rename or delete your current H2 database file: /databases/mah2.h2.db Start Mango and you will now have a new clean database. You can login with admin | admin and complete the restore process. Be sure you do not restore a database that is from an older version of Mango.