Sample of customizing venue/organizer list output re https://theeventscalendar.com/knowledgebase/listing-venues-and-organizers/

simple-feat-img-tweak.php

function add_featured_img( $item ) {
    $img = get_the_post_thumbnail();
    return str_replace( '<li>', '<li>' . $img, $item );
}

add_filter( 'TEC_VenueOrganizer_List.list.item', 'add_featured_img' );