C# EF Code First Seeding Data - Keeps Adding (Instead of updating)

C# EF Code First Seeding Data - Keeps Adding (Instead of updating)

I have a list of type User and when I try to seed my db to reflect
updates, it is simply adding all the entries again. I will share my code I
am executing in my Seed() method. I wish to just update the records (but
keep the add functionality), if they already exist. Any thoughts?
List<User> users = new List<User>();
users.Add(new User { FirstName = "Dee", LastName = "Reynolds" });
users.Add(new User { FirstName = "Rickety", LastName = "Cricket" });
users.ForEach(b => context.Users.AddOrUpdate(b));