Add Message Received to ListBox

I'm trying to do a simple WebSocket Server in C# that will communicate with a Client in JavaScript, the code I am using is this:

using System;
using System.Windows.Forms;
using WebSocketSharp;
using WebSocketSharp.Server;

namespace MyProgram
{
    public partial class Form1 : Form
    {
        public Form1()
        {
            InitializeComponent();
        }

        private void button1_Click(object sender, EventArgs e)
        {
            var wssv = new WebSocketServer(8081);

            wssv.WaitTime = TimeSpan.FromSeconds(3);

            wssv.AddWebSocketService<NFP>("/");

            wssv.Start();
        }
    }

    public class NFP : WebSocketBehavior
    {
        protected override void OnMessage(MessageEventArgs e)
        {
            Console.WriteLine(e.Data);

            Send("Received");
        }

        protected override void OnError(ErrorEventArgs e)
        {
            //Console.WriteLine(e.Exception);
        }

        protected override void OnClose(CloseEventArgs e)
        {
            //Console.WriteLine(e.Code);
        }
    }
}

Now I was wondering, how do I send the message received at OnMessage for the ListBox that is on Form1 already open?

Start with the Form1 code and NFP.OnMessage shown in the issue, then trace how the existing ListBox can receive e.Data from the WebSocket handler. Done means a message received by OnMessage is displayed in the already-open ListBox; verify the behavior with a JavaScript client sending a message.