From the 'campaigns' page, click on the name of the campaign that you are interested in. This will direct you to a summary page that will show the call history for that campaign. Alternatively, you can click on the 'history' tab at the top of the page.
Click on the 'history' tab at the top of the page. This will allow you to select a date range. After you have selected the dates for the call history that you would like to export, click the 'download' button. A history report will be downloaded to your computer as a CSV file.