Hey Brendan,
Let’s say your theme path is this:
/wp-content/themes/twentysixteen
If you follow the steps of our Themer’s Guide, you can make a new folder within that theme where all customized Events Calendar templates live. This folder should be called tribe-events, like this:
/wp-content/themes/twentysixteen/tribe-events
For Filter Bar-specific files, those go in ANOTHER subfolder WITHIN /tribe-events, called /filter-bar.
So if you’re trying to make a custom version of Filter Bar’s filter-view-horizontal.php file, you could make a customized version of that file in your theme at this full path:
/wp-content/themes/twentysixteen/tribe-events/filter-bar/filter-view-horizontal.php
Learn more about this on the Themer’s Guide here ? https://theeventscalendar.com/knowledgebase/themers-guide/
Cheers,
George