Missing display option in dashlet
The option you're looking for isn't under the Access tab.  It's below all the tab data.  See the attached screenshot.

Note that most reports do NOT offer the ability to view a chart - make sure your report does!  If you'd like to test, use the "Contribution Summary" report, which supports charts.

After you've changed the view, press the "Update Report" button, and on the dashboard, press "Refresh Dashboard Data" and you should be in business.