Contact Page - Add New TextBox

I am trying to add a new text box in a contact form that I use, but I know 0 C#. I know this is probably easy once you know how to do it but I don't. Any help would be great or even a point in the right direction. I have posted my code below.

<%@ Control Language="C#" AutoEventWireup="true" Inherits="NopSolutions.NopCommerce.Web.Modules.ContactUsControl" CodeBehind="ContactUs.ascx.cs" %> <%@ Register TagPrefix="nopCommerce" TagName="SimpleTextBox" Src="~/Modules/SimpleTextBox.ascx" %> <%@ Register TagPrefix="nopCommerce" TagName="EmailTextBox" Src="~/Modules/EmailTextBox.ascx" %> <%@ Register TagPrefix="nopCommerce" TagName="Topic" Src="~/Modules/Topic.ascx" %> <div class="contact-form"> <div> <nopCommerce:Topic ID="topicContactUs&qu ...