Editting English language file

I have been looking all day at a possible solution, but stil haven’t found one.
I’m trying to edit certain words in this plugin, in English. So I’m not looking for a translation file.

According to the FAQ, I can add a string to the functions.php file of my template, but that only gives me an error.
When I check the language folder of the plugin, I can’t seem to find the regular enligsh .mo or .po file?

That would really be all I need so I can make the few edits needed.
Any ideas on how to find or accomplish this?

https://www.ads-software.com/plugins/the-events-calendar/