Use the 'Refresh' button near to the 'Export from date' field in the top of the screen to refresh and update the preview tab results.
Use this button when:
You have updated the export from date.
You have updated details in Synergy or MYOB in another tab.
You have skipped a group, or items within a group then. On 'Refresh' those skipped items are saved to the skipped items tab.