The following steps will guide you to the page where this can be updated and what each option does.
Click the Admin Cogs icon.
Click Flash Reports, then click Site Reports.
To select the flash to be updated click the Edit button, and click into the Details tab.
Scroll down to the Data Import Method section and select from the below:
Combine with existing: Keeps adding to the existing data. Or if 1 file contains multiple till references using the same PLU/Epos codes and is for 1 flash report it will combine the the sales into 1 line.
Overwrite existing: Overwrites existing values but it will not remove any that may already be there.
Clear all, then insert: All data is removed and then new records added.
Click Save.