Unable to change default date

I’m trying to set the default date when the events open to September 2016 and found this useful page:

https://theeventscalendar.com/knowledgebase/set-calendar-to-show-specific-month/#dl_file-default-month-php

However, when I add this snippet of code to the end of functions.php, my site stops working. If I comment out the “<?php” and add_action call, i.e. just add the function to functions.php then it loads but of course the default date doesn’t change.

I’m not that familiar with php so not exactly sure what’s going on here but suspect this is a WordPress generic question, not a problem as such with the event calendar.

Any suggestions appreciated.

https://wordpress.org/plugins/the-events-calendar/