Receiving HEX Via TCP

I need to convert a string that has been converted to HEX and sent via TCP to string.

I tried the 2 forms below and I only get illegible string:

public async void HandleConnections(TcpClient client)
{
  using (var networkStream = client.GetStream())
  {
    using (var reader = new StreamReader(networkStream))
    {

    returndata = await reader.ReadLineAsync();

    }

  }

}

public async void HandleConnections(TcpClient client)
{
    byte[] bytes = new byte[client.ReceiveBufferSize];

    string returndata = Encoding.UTF8.GetString (bytes);

    Console.WriteLine (returndata);
}