To restore from an internal backup, tap Options , then Settings. Go to Backup, then Manage Backups. Find a backup from before you noticed the changes. To restore it, tap the ellipses on the right side and select Restore. If the backup is from a user with a different name than the one you are currently in, simPODD will ask which user you want to restore it to.
Internal backups are only stored inside simPODD. If you accidentally delete simPODD or the device is damaged, you will also lose these backups. However, simPODD also syncs automatically with iCloud, and you can manually save and export backups. For instructions, please see Backup and restore simPODD.