Export/Import tab provides the ability to Import Data from Report Builder app using JSON. If you did not use Report Builder app before spliting it to Timesheet Builder and Report Builder, you can ignore this tab, as there is no data to be uploaded.
...
How to export data from Report Builder and import it to Timesheet Builder?
Important information
Please note, that existing customizations of Configuration will be replaced or set to default, if Export/Import option is used after taking some actions, such as adding global calendars, setting possibility to use secured worklogs (for Data Center version only). It means, if you added some global calendars on Dates tab or if you if you set “Allow secured worklogs usage” on Worklogs tab (for Data Center version only), calendars will be deleted and it will not be allowed to use secured worklogs option after importing data, and Administrator should add global calendars and allow secured worklogs usage again.
...