How do I correctly reference uriparser?

typeof(UriParser)

but I get a compiler error:

The type or namespace name 'UriParser' could not be found (are you missing a using directive or an assembly reference?)

The following lines are included above the namespace:
using System; 
using System.Text;
using System.Drawing; 
using System.Collections; 
using System.ComponentModel; 
using System.Windows.Forms; 
using System.IO; 
using System.Reflection;

What am I missing? How can I correctly include UriParser in my project?

Thank you.
 
The entire procedure is to do with removing an unescaped slash from the url:
public void LeaveDotsAndSlashesEscaped()
{
    var getSyntaxMethod =
        typeof(UriParser).GetMethod("GetSyntax", BindingFlags.Static | BindingFlags.NonPublic);
    if (getSyntaxMethod == null)
    {
        //throw new MissingMethodException("UriParser", "GetSyntax");
    }
 
    var uriParser = getSyntaxMethod.Invoke(null, new object[] { "http" });
 
    var setUpdatableFlagsMethod =
        uriParser.GetType().GetMethod("SetUpdatableFlags", BindingFlags.Instance | BindingFlags.NonPublic);
    if (setUpdatableFlagsMethod == null)
    {
        //throw new MissingMethodException("UriParser", "SetUpdatableFlags");
    }
 
    setUpdatableFlagsMethod.Invoke(uriParser, new object[] { 0 });
}