Hi Jordane,
Thanks for taking the time to reach out! If you’ve made changes to the original single-event.php file that need to be reversed, you can re-download a fresh copy of Events Calendar PRO from your account’s Downloads page at any time. Simply download the plugin archive, unzip the files to any directory on your computer, and upload your new copy of single-event.php to your web server, replacing the previous copy in your plugin directory.
While customizations of this type are beyond the scope of what support services we can provide, I’m happy to try and point you in the right direction here! This forum thread provides some more information on customizing the display of related events, which you may find helpful as you’re getting started:
https://theeventscalendar.com/support/forums/topic/exclude-categories-from-related-events/
I hope that helps to get you on your way here! 🙂 Thanks again, and please don’t hesitate to follow up if you should have any other questions!