I programmed that add-on for Zino at the time and implemented it on his server.
Please note that due to the way Discord works, it requires a Linux daemon running on your server at all times. If you can handle Linux yourself, I can just give you instructions on how to implement it.
Otherwise, I can implement it for you but I need your Linux credentials (the username and password for the Linux user that PHP is running under).
If you do not have access to your Linux shell or cannot run daemons there (due to your hosting configuration), then implementing the add-on is not possible.
I attached 2 screenshots - one is the add-on configuration screen. You will need to enter your Discord server credentials there as well as map the Discord roles to the XF user groups.
As you can see in the configuration screen, you need to create a Discord bot which will communicate with the add-on. If you do not know how to create a Discord bot, once again I can do it for you providing I have access to your Discord server.
The second screenshot is the user details page, where users connect or disconnect their Discord account to your forum. When they connect, they will be presented with a Discord authentication screen (OAuth2) so as to give your forum permission to read their user roles.
Feel free to PM if interested.
All the best,
Gigi