Events Calendar Buy button change

functions.php

<?php


add_filter( 'tribe_tickets_buy_button', 'rt_mt_buy_now_rename', 10, 4 );

function rt_mt_buy_now_rename( $html, $parts, $types, $event_id) {
    $find    = 'Buy Now!';
    $replace = 'Register';

    $html['button'] = str_replace( $find, $replace, $html['button'] );

    return $html;
}