inc/admin.report.functions.php contains an action hook you could use to create your own customised sales report.
If you want to do that , I would suggest something like the following.

use the action hook like so (in your functions.php for example)

add_action('wppizza_custom_report', 'my_custom_report');
function my_custom_report($dataset){
/* 
i would suggest you start off by copying the  wppizza_report_export function - i.e the function the 'wppizza_custom_report' action hook is in  - into this custom function (without that action hook) and edit as a required 
*/
}