สอบถามเกี่ยวกับการตั้งค่า autoincrement รหัสบันทึก C#

private void button2_Click_1(object sender, EventArgs e)
        {
           
                using (SqlConnection conn = new SqlConnection())
                {
                    Config config = new Config();
                    string constring = config.ConnString;
                    String name = comboBox1.SelectedItem.ToString();
                    String color = comboBox2.Text.ToString();
                    String valuedb = txtBoxDIV.Text.ToString();
                    String numbermat = matche1.Text.ToString();
                    String DayDate = dateTimePicker1.Text.ToString();
                    String Priceexd = txtAllPriceEND.Text.ToString();

                    conn.ConnectionString = constring;
                    conn.Open();
                    string sql = "INSERT INTO tbl_sinkar (ชื่อสินค้า,สี,จำนวน,เครื่องที่ผลิต,วันที่ผลิต,ต้นทุนต่อก้อน) values('" + name + "', '" + color + "', '" + valuedb + "', '" + numbermat + "', '" + DayDate + "', '" + Priceexd + "')";
                    SqlCommand com = new SqlCommand(sql, conn);
                    com.ExecuteNonQuery();
                    MessageBox.Show("Success Save In Database");
                    
                  
                }
                

            Form3 f1 = new Form3();
            f1.Show();   
            
        }

public partial class Form3 : Form
    {

        public Form3()
        {
            InitializeComponent();
        }

        private void Form3_Load(object sender, EventArgs e)
        {
           
            using (SqlConnection conn = new SqlConnection())
            {
                Config config = new Config();
                string constring = config.ConnString;
                conn.ConnectionString = constring;
                conn.Open();

            }
            ShowdataMaterail();

        }

        private void ShowdataMaterail()
        {
            using (SqlConnection conn = new SqlConnection())
            {
                Config config = new Config();
                string constring = config.ConnString;
                conn.ConnectionString = constring;
                conn.Open();

                string sql = "SELECT * FROM tbl_sinkar";
                DataSet ds = new DataSet();
                SqlDataAdapter da = new SqlDataAdapter(sql, conn);
                da.Fill(ds, "tbl_sinkar");
                dataGridView1.DataSource = ds;
                dataGridView1.DataMember = "tbl_sinkar";

            
                    
            }
        
        }

        private void Update1_Click(object sender, EventArgs e)
        {
            using (SqlConnection conn = new SqlConnection())
            {
                Config config = new Config();
                string constring = config.ConnString;
                conn.ConnectionString = constring;
                conn.Open();

                string sql = "UPDATE tbl_sinkar SET ชื่อสินค้า = '"+textBox2.Text.Trim()+
                "', สี = '" +textBox3.Text.Trim()+
                "', จำนวน = '" + textBox4.Text.Trim() +
                "', เครื่องที่ผลิต = '" + textBox5.Text.Trim() +
                "', วันที่ผลิต = '" + textBox6.Text.Trim() +
                "', ต้นทุนต่อก้อน = '" + textBox7.Text.Trim() +
                "' WHERE รหัสการบันทึก ='"+txt1.Text.Trim()+"' ";
                SqlCommand com = new SqlCommand(sql, conn);
                com.ExecuteNonQuery();
                MessageBox.Show("แก้ไขข้อมูลเรียบร้อย");
            } 
            ShowdataMaterail();
            
        } 

        private void De1_Click_1(object sender, EventArgs e)
        {
            
            using (SqlConnection conn = new SqlConnection())
            {
                Config config = new Config();
                string constring = config.ConnString;
                conn.ConnectionString = constring;
                conn.Open();

                String sql = "DELETE FROM tbl_sinkar WHERE รหัสการบันทึก ='" + txt1.Text.Trim() + "' ";
                SqlCommand com = new SqlCommand(sql, conn);
                com.ExecuteNonQuery();
                MessageBox.Show("ลบข้อมูลสำเร็จ");
            }
            ShowdataMaterail();


        }

        private void dataGridView1_CellMouseClick(object sender, DataGridViewCellMouseEventArgs e)
        {
            if (e.RowIndex == -1) return;
            txt1.Text = dataGridView1.Rows[e.RowIndex].Cells[0].Value.ToString();
            textBox2.Text = dataGridView1.Rows[e.RowIndex].Cells[1].Value.ToString();
            textBox3.Text = dataGridView1.Rows[e.RowIndex].Cells[2].Value.ToString();
            textBox4.Text = dataGridView1.Rows[e.RowIndex].Cells[3].Value.ToString();
            textBox5.Text = dataGridView1.Rows[e.RowIndex].Cells[4].Value.ToString();
            textBox6.Text = dataGridView1.Rows[e.RowIndex].Cells[5].Value.ToString();
            textBox7.Text = dataGridView1.Rows[e.RowIndex].Cells[6].Value.ToString();
            txt1.Enabled = false;
            

        }

        
    }