I did that about a week ago. There is an option in the app settings to move your installation. Since you did not do this, check here: C:\Users\XXXX\AppData\Local\Packages\Microsoft.FlightSimulator_8wekyb3d8bbwe\LocalCache
There should be a file called UserCfg.opt. Open that with notepad and check the last line. It points to your installation. Change it to the location that you moved your installation. It should work now.
Edit: If you named your new drive the same as the old one, then there should be something else that is wrong. In that case, I don’t know…
Edit No 2: Try the options to repair or reset your installation. I assume you know were these are located.