How to Change Read Only Properties With Reflection

//Declare Namespace
using System;
using System.Reflection;
namespace ChangeReadonlyProperty
{
    class Program
    {
        static void Main()
        {
            DemoClass demoClass = new DemoClass();
            Console.WriteLine("String readonly value : {0}", demoClass.GetVal());
            FieldInfo fieldInfo = typeof(DemoClass).GetField("strVal", BindingFlags.Instance | BindingFlags.NonPublic);
            //User value
            Console.WriteLine("Please enter the value");
            string strUserval = Console.ReadLine();
            //Check and assign default value if null value from the User
            strUserval = strUserval == string.Empty ? "No Value" : strUserval;
            //Change the read only value with user value
            if (fieldInfo != null)
                fieldInfo.SetValue(demoClass, strUserval);
            Console.WriteLine("User value : {0}", demoClass.GetVal());
            Console.ReadKey();
        }
    }
    public class DemoClass
    {
        // declare the readonly property
        private readonly string strVal = "Demo";
        // method for get the value
        public string GetVal() { return strVal; }
    }
}