Add button to call PHP function

I’ve written a small report plugin for WooCommerce for a friend of mine but he want’s the data to be exported in CSV format. I have found an article that lets me pass the results from the query and export it in CSV format ( http://kevinjmcmahon.net/articles/24/exporting-mysql-table-data-to-excel-using-php/ ). I’m lost on how to add a button to my admin page that when a user clicks it, will then run my CSV export function.