Orbx as an official partner install their products into the Official\OneStore folder, you can try removing the current installation. Make sure the sim isn’t running, look for orbx-airport-eglc-london-city folder and delete it. Start the sim and hopefully, you should be able to attempt the install again.
Example location: Yours will be different depending on what store you used…
C:\Users\youruserid\AppData\Local\Packages\Microsoft.FlightSimulator_8wekyb3d8bbwe\LocalCache\Packages\Official\OneStore\orbx-airport-eglc-london-city