Here is a United Airlines logo wallpaper, that is is similar to what they have on their corporate computers.
Installation
1. Open your simulator and load a flight in the Fenix A320 Block 2
2. Open your browser and go on this website: http://localhost:8083/
3. Open the "Settings" app on the website
4. Press "Select image or drop it here" - either drop the image or browse it
5. If you wish to remove the background, press "reset background"