To reset Microsoft Store, open Settings > Apps > Apps and features > Search for Microsoft Store > Advanced options > Use the Reset button.
To reset the cache for Microsoft Store you can also use Windows Settings or use the built-in command-line tool known as WSReset.exe.
You can also run CMD as administrator, type WSReset.exe and hit Enter.
Alternatively, in the Start search, type wsreset.exe.
Then, restart MSFS and check the Content Manager. You should once again have access to the C337 and be able to download/install so that it shows up again for you.
Cheers!