Be sure to run as administrator, otherwise the object already exits problem will occur.

Change the file name to Web.config, start the command line tool Tools -> Command Line, enter aspnet_regiis -pef "**Target String**" " **Target Address(e:\)** . Afterward, change Web.config back to App.config and it can be accessed.
We need the ConfigurationManager class when accessing. Use VS shortcut ctrl+. to use NuGet for quick deployment.

https://blog.csdn.net/u011981242/article/details/51090487