How to connect ClickFrog file to cs-cart using PHP?

Question

CMS

Hello, the question is about connecting a php file to a marketplace site built on cs-cart.
The clickfrogru_tcp.php file is located in the root of the site, and a copy is in the my_changes module, but they write that they do not see this file connected.
How to connect ?
They ask to connect to the root init.php file, but I know that this is not the correct way to include a php file.
Message from Clickfrog:
"Total.
1. php code clickfrog needs to be connected
The code is loaded, requests are coming, for connections, add the line
include_once $_SERVER['DOCUMENT_ROOT'].'/clickfrogru_tcp.php';
immediately after <?php or <? for everything landing pages.
There is no site with such cms at hand to look as an example.'"

How to connect it and make available "site/clickfrogru_tcp.php". I tried to create func.php in which I wrote this file, but I'm not sure that I created it there and it's still not visible "site/clickfrogru_tcp.php" in this path.
PLEASE HELP