When a tablet starts, Vitess checks the value of the --restore_from_backup command-line flag to determine whether to restore a backup to that tablet.

• If the flag is present, Vitess tries to restore the most recent backup from the Backup Storage system when starting the tablet.
• If the flag is absent, Vitess does not try to restore a backup to the tablet. The MYSQL database associated with the tablet will be empty.

For more information on restoring and managing backups please follow the link here.