Spoofing an IP address in C# typically involves creating a web request and modifying the headers to include the desired IP address. Here is an example of how this could be done:

using System;
using System.Net;
using System.IO;

namespace ConsoleApp
{
    class Program
    {
        static void Main(string[] args)
        {
            // Create a web request to the target website
            HttpWebRequest request = (HttpWebRequest)WebRequest.Create("http://www.example.com");

            // Set the desired IP address as the value of the "X-Forwarded-For" header
            request.Headers["X-Forwarded-For"] = "1.2.3.4";

            // Send the request and get the response
            HttpWebResponse response = (HttpWebResponse)request.GetResponse();

            // Print the response status code
            Console.WriteLine(response.StatusCode);

            // Close the response stream
            response.Close();
        }
    }
}

It's important to note that spoofing an IP address does not guarantee that the website will treat the request as if it's coming from the specified IP address. Many websites have measures in place to detect and prevent IP address spoofing, and some may even block requests that include forged IP addresses. Additionally, modifying headers in this way may violate the terms of service for the website you are accessing, so it's important to use this technique carefully and only for legitimate purposes.