If you have it installed on your phone, you can sideload it using apps2fire. Go in the fire TV settings, select "my fire tv", then go in "developers option" and finally, enable both options there, allow ADB and installing apps from unknown sources. Go in the apps2fire app, go to the "install" tab (the last one) then search for your device. Go back to the first tab, find the app you want to install, select it, then tap install. I can't guarantee that the app will work, as I don't think it's even in the android tv play store, and the app is made for screens in portrait mode. If it works some menus will probably only accept touch input, though you can sidestep that by using a Bluetooth mouse.