How do i insert data in a row based on whether a column is correct?

Question

I want to be able to enter data to amount based on whether the social number is correct. I always get the error message SqlException: Cannot insert explicit value for identity column in table 'Customers' when IDENTITY_INSERT is set to OFF.. I have tried to make a sql command to the database and set Identity to ON, but I still get the same error. Is it possible to do what I want to do?

My Class

public class AddAmount : IAddAmount
    {
        private readonly ApplicationDbContext _db;

        public AddAmount(ApplicationDbContext db)
        {
            _db = db;
        }

        public void Insert(int number)
        {
            Console.WriteLine("Add your amount you would like to insert: ");

                try
                {

                var addAmount = _db.Customers.SingleOrDefault(x => x.SocialNumber == number);
                addAmount.Amount = Convert.ToInt32(Console.ReadLine());
                 _db.Database.ExecuteSqlInterpolated($"SET IDENTITY_INSERT dbo.Customers ON");
                _db.Add(addAmount);
                _db.SaveChanges();

                }
                catch (Exception)
                {

                    throw;
                }
        }

    }