Update elements in a collection, using LINQ

update-collection.cs

using System;
using System.Collections.Generic;
using System.Linq;

namespace UpdateCollection
{
	class Program
	{
		static void Main(string[] args)
		{
			try
			{
				var people = new List<Person>()
				{
					new Person() { FirstName = "Robert", LastName = "Jones" },
					new Person() { FirstName = "William", LastName = "Smith" }
				};

				Console.WriteLine("Before:");
				foreach (var person in people) Console.WriteLine($"\tHello, {person.FirstName} {person.LastName}!");

				people.Where(p => p.FirstName == "Robert").ToList().ForEach(x => x.FirstName = "Bob");
				people.Where(p => p.FirstName == "William").ToList().ForEach(x => x.FirstName = "Bill");

				Console.WriteLine("After:");
				foreach (var person in people) Console.WriteLine($"\tHello, {person.FirstName} {person.LastName}!");
			}
			catch (Exception ex)
			{
				Console.WriteLine(ex.Message);
			}
		}
	}

	public class Person
	{
		public string FirstName { get; set; }
		public string LastName { get; set; }
	}
}