How to create a device identity for IotHub in VS-17

Question

I am beginner of IOT and i learning to creating the app with IotHub by seeing the tutorial from this link:

 https://docs.microsoft.com/en-us/azure/iot-hub/iot-hub-csharp-csharp-getstarted

i created the IotHub using Azure but I can't create an identity of my device.

  Here's my code : 

   

using System;
using System.Threading.Tasks;
using Microsoft.Azure.Devices;
using Microsoft.Azure.Devices.Common.Exceptions;
namespace DeviceIdentity
{
    class Program
    {
        static  RegistryManager Registrymanager;
        static string connectionString = "{iot hub connection string}";
        private static async Task AddDeviceAsync()
        {
            string deviceId = "myFirstdevice";
            Device device;
            try
            {
                device = await Registrymanager.AddDeviceAsync(new Device(deviceId));
            }
            catch (DeviceAlreadyExistsException)
            {
                device = await Registrymanager.GetDeviceAsync(deviceId);
            }
            Console.WriteLine("Generated device key: {0}", device.Authentication.SymmetricKey.PrimaryKey);
        }
        static void Main(string args[])
        {
              Registrymanager =RegistryManager.CreateFromConnectionString(connectionString);
            AddDeviceAsync().Wait();
            Console.ReadLine();
        }
    }
}