Follow the instruction below:
1) Don’t forget to take a backup of the file prior to any change.
2) Copy single-session.php to wp-content/themes/fudge2-child
3) Open wp-content/themes/fudge2-child/ single-session.php
4) Around line number 174, you can find:
<?php echo $session_registration_code; ?>
5) Please change this to:
<?php echo do_shortcode($session_registration_code); ?>
6) Save the file.