Load a custom ticket selector template from your theme (or child theme) root directory.

functions.php

<?php
//* Please do NOT include the opening php tag, except of course if you're starting with a blank file

add_filter ('FHEE__EE_Ticket_Selector__display_ticket_selector__template_path', 'my_custom_ticket_selector_template_location');

function my_custom_ticket_selector_template_location(){
    return get_stylesheet_directory() . '/ticket_selector_chart.template.php';
}