Increment quantity if have value from textbox in datagrid c#

Question

Some little help.

 

Need if  exist in datagrid value from textbox1 ( column name: bar_code) to increment cell kolicina(quantity eng.) + 1

private void prijavaAction()
        {

            int sno = dataGridView1.Rows.Count + 1;

            SqlConnection con = new SqlConnection(cs);

            if (textBox1.Text.All(char.IsDigit))

            {
                string queryString = "select bar_kod, ime, cijena_sa_porezom from roba_usluge WHERE bar_kod = '" + textBox1.Text + "'";// pronaci artikl u bazi
                using (SqlConnection connection = new SqlConnection(cs))
                {
                    SqlCommand command = new SqlCommand(queryString, connection);
                    connection.Open();
                    SqlDataReader reader = command.ExecuteReader();


                    var itemAndPrice = textBox1.Text;

                    if (reader.Read())
                    {

                        var index = dataGridView1.Rows.Add();
                        dataGridView1.Rows[index].Cells["redni_broj"].Value = index + 1;
                        dataGridView1.Rows[index].Cells["bar_kod"].Value = reader["bar_kod"].ToString();
                        dataGridView1.Rows[index].Cells["naziv_artikla"].Value = reader["ime"].ToString();
                        dataGridView1.Rows[index].Cells["cijena"].Value = reader["cijena_sa_porezom"].ToString();
                        dataGridView1.Rows[index].Cells["kolicina"].Value = "1";


                        foreach (DataGridViewRow g1 in dataGridView1.Rows)
                        {


                            g1.Cells["ukupno"].Value = (Convert.ToDouble(g1.Cells["kolicina"].Value) * Convert.ToDouble(g1.Cells["cijena"].Value)).ToString("0.00");
                               g1.Cells["kolicina"].Value = Convert.ToInt32(g1.Cells["kolicina"].Value) + 1;
                        }
                    }
                    else
                    {
                        MessageBox.Show("Bar kod ne postoji u bazi!", "Obavještenje", MessageBoxButtons.OK, MessageBoxIcon.Information);
                        textBox1.Text = "";
                    }
                }
            }
            else
            {
                MessageBox.Show("Bar kod ne postoji ili nije bar kod!", "Obavještenje", MessageBoxButtons.OK, MessageBoxIcon.Information);
                textBox1.Text = "";
            }

}