To make changes to the header (for online reports) or the cover (at PDF reports) click the "Edit the header" button at the top of the draft report.
There you can choose to show/hide the following items on your PDF cover page or online report header:
Compare date range
Note: If you use Shareable linked reports, make sure the "Date range" field is enabled to allow your client to edit the date range in the export. Don't know what shareable linked reports are? Read more about them here.