insert csv base on line

Question

Hi, need help, how to insert into the database based on the last row in CSV. for example, I have 500 lines, all 500 lines already insert into the database. How to do if the row change to the 501 lines and the insert start from line 501. I want to replace it from delete, to insert from line 501. Help me please

if (LWT > 0)
{
    Console.WriteLine("There are no changes in lastWriteTime CSV file");
    var del1 = "delete from result";
    var cmd11 = new NpgsqlCommand(del1, conn);
    cmd11.ExecuteNonQuery();
}
else
{
    Console.WriteLine("There are changes lastWriteTime in CSV file");
    var lf2 = "insert into listfile(filename)values(@filename)";
    var cmd3 = new NpgsqlCommand(lf2, conn);
    cmd3.Parameters.AddWithValue("filename", Convert.ToString(file));
    string filename = cmd3.Parameters["@filename"].Value.ToString();
    Console.WriteLine("Record inserted successfully. filename = " + file);
}