Filenotfoundexception: Could Not Load File or Assembly 'System. Configuration. Configurationmanager,

I am trying to connect to oracle database from .net core 3.1 using ado.net here's my code

private OracleConnection GetOracleConnection()
{
            string conString = "Data Source=Q550.adr.XXXX.com;Persist Security,Info=True;User ID=XXXX;Password=CCC39";
            OracleConnection con = new OracleConnection(conString);
            return con;
}

but when this function executes following exception occured at line number 2

System.TypeInitializationException: 'The type initializer for 'OracleInternal.Common.ProviderConfig' threw an exception

FileNotFoundException: Could not load file or assembly 'System.Configuration.ConfigurationManager, Version=4.0.2.0, Culture=neutral, PublicKeyToken=cc7b13ffcd2ddd51'. The system cannot find the file specified. **

Can anyone tell me what's happening ??