EOS is a little bit different compared to other Distributions in terms of installing applications. Is the application available somewhere so i can work out a exact procedure for installation for you?
This is an application that I downloaded from a publisher's website with personal code that was provided to me. The app isn't available anywhere other than on the publisher's website. I downloaded the .zip file, unzipped it into the Downloads folder. A new folder has appeared, inside it there's another folder and it's inside this folder that the .desktop application to be installed is located.
In general, a file ending with .desktop is just a description used by the operating system to have a Application Entry available at the usual places.
The .desktop has to be placed under ~/.local/share/applications. Open it with a Editor and point the Exec line to the unpacked executable of the application.
Unfortunately without the files i’m unable to provide detailed steps, so you’re a little bit on your own here