Please a hint for a little change on the plugin

Hi

i need to make a little change on the output of [fullcalendar] (i know, i shouldnt, but… customers).

i see that you make a ajaxcall on loading the data
https://prdev6.info/wp-admin/admin-ajax.php?action=WP_FullCalendar&type=event&month=1&year=2017&start=2017-03-06&end=2017-03-13&_=1487974116336

but for the live of me, i can’t figure out where this ajax function goes. it looks easy:
wp-fullcalendar.php
add_action(‘wp_ajax_WP_FullCalendar’, array(‘WP_FullCalendar’,’ajax’) );

But whatever i do in there, in the ajax function, does not seem to have any effect.

can you give me a tip in what part your plugin pulls the data?

ThankS!!