IIS Express - Retained an incorrect value (somewhere, but where)

I changed the "applicationurl" value for iisExpress in launchsettings.json (incorrectly).

It was set to...

"applicationUrl": "http://localhost:64522"

...but I changed it to...

"applicationUrl": "http://localhost:64522/MyPage"

...before changing it back.

Now, when I navigate to http://localhost:64522/MyPage I get an application pool error.

Where has IIS Express added this value? I want to remove it.

Edit 1:

I have checked every applicationHost.config on my machine but there is no mention of this URL.

Edit 2:

The error I get is:

"IIS Express AspNetCore Module V2":

Only one in-process application is allowed per IIS application pool. Please assign the application '/LM/W3SVC/34/ROOT/MyPage' to a different IIS application pool.

Failed to start application '/LM/W3SVC/34/ROOT/MyPage', ErrorCode '0x80004005'.