Hi Chris,
I can tell you where the files are, but there is no way to modify this without modifying the plugin, which means updates are lost when the plugin is updated.
The other option is to create a standalone widget with our coding as the base.
First you will have to modify the Admin to get Organizers Instead of the Taxonomy in this file for the Event List Widget:
events-calendar-pro\src\admin-views\widget-admin-advanced-list.php
Then you would have to modify this file to change the taxonomy query to get only events with the organizer id here:
events-calendar-pro\src\Tribe\Advanced_List_Widget.php
That can help get you started, but that is about all we can do to help out on a customization unfortunately.
Cheers