Using contact/notify in GIOZ theme

Downloaded the GIOZ theme and I’m having difficulty figuring out how to make the contact form and notify button work properly. Instruction say its “easy” but fails to give “easy” instruction. (Also possible that my basic PHP is not as good as it should be).
This is the instruction:

As default the subscribe form is set as Txt File.
To change it, open the file php/notify-me.php and clear appropriate service settings. Also you should insert certain data - APIKEY, USERNAME, LISTID…

In opening the php file, changing the above is simply not that straightforward.
Googling ways to do it has not come up with any good pages. I don’t mind putting the research time into it, but I’ve already wasted 3 hours and was hoping someone knows of a link or page that may be able to help me figure out how to fill this in.
I have attempted to email the ‘author’ but considering the web link I found is not functional, I am not confident of a reply any time soon.
All guidance is very much appreciated.