It is probably on the c drive but directory on
Navigate to, C:\Users\profilename\Appdata\Local\Packages\Microsoft.FlightSimulator_8wekyb3d8bbwe\LocalCache
(Note that profilename is the name of your own making)
If you cannot see Appdata folder than it is probably hidden( for this is by default in windows settings) this you can unhide. Under screen → options–> see pictures
If it looks like this
Than follow steps 1,2 and 3
Hope u find can find UserCfg.opt file now