Backups are automatically created when your data changes (once for the day Outbank was opened).

If you want to manually create a backup, please follow these steps:

Menu > Outbank > Settings > Security > Create backup

The backups will be saved under ~/Library/Containers/com.stoegerit.outbank.osx/Data/Documents/backups/

To open the backup folder click on  'File' > 'Backups' or go to the Settings of Outbank and select 'Security' > 'Show backups'.