Example appsettings:

{
  "Logging": {
    "LogLevel": {
      "Default": "Warning"
    }
  },
  "AllowedHosts": "*"
}

Create MyConfig name class and;

using Microsoft.Extensions.Configuration;
static class ConfigurationManager
{
    public static IConfiguration AppSetting { get; }
    static ConfigurationManager()
    {
        AppSetting = new ConfigurationBuilder()
                .SetBasePath(Directory.GetCurrentDirectory())
                .AddJsonFile("appsettings.json")
                .Build();
    }
}

Now you can use it like :

string value = ConfigurationManager.AppSetting["value_Key"];