Hi Ali,
Welcome
I suggest you
- Close the sim
- Delete the content.xml file it´s located here
%localAppData%\Packages\Microsoft.FlightSimulator_8wekyb3d8bbwe\LocalCache
- Start the sim (the content xml file will be recreated)
- Close the sim again, open the NNC and install the AIRAC (if its still not installed)
Cheers
Ian