Hi,

In your theme functions.php file add following actions:

// Opens events in same window
add_action('wp_footer', function() {
    ?>
    <script type="text/javascript">
        if (typeof jQuery.stecExtend === 'function') {
            jQuery.stecExtend(function (master) {
                master.eventsHandler.eventToggle = function ($event) {
                    window.open($event.find('.stec-layout-event-single-page-link').attr('href'), '_self');
                    return false;
                };
            });
        }
    </script>
    <?php
});

// Adds link before the event content. Replace href url with the actual link to the calendar
add_action('stec_single_before_content', function() {
    ?>
    <a href="//link-to-calendar-here"><?php _e('Back to calendar', 'stec'); ?></a>
    <?php
});

// Adds link after the event content
add_action('stec_single_after_content', function() {
    ?>
    <a href="//link-to-calendar-here"><?php _e('Back to calendar', 'stec'); ?></a>
    <?php
});