Example of how to automatically check the radio button within the ticket selector using jQuery.

example.php

<?php //Please do not include the opening PHP tag if you already have one 

function tw_ee_radio_button_checked() {
  wp_add_inline_script( 
    'ticket_selector',
    'jQuery( document ).ready(function($) {
     	$(".tkt-slctr-tbl").each(function(){		    
	    if( $(this).find(".ticket-selector-tbl-qty-slct:radio").length == 1 ){
	    	$(this).find(".ticket-selector-tbl-qty-slct:radio").prop("checked", true);
	    }
	});
    });'
  );
}
add_action( 'wp_enqueue_scripts', 'tw_ee_radio_button_checked', 11 );