How to update only one table column in datagridview

string connectionString = null;
            connectionString = ConfigurationManager.ConnectionStrings["AccessConnectionString"].ConnectionString;
            con.ConnectionString = connectionString; 
            string medicinename = dataGridView1.SelectedRows[0].Cells["Medicine_Name"].Value.ToString();
            
            DialogResult dialogResult = MessageBox.Show("Are you sure you want to insert data", "Data insert Confirmation", MessageBoxButtons.YesNo, MessageBoxIcon.Information);
            if (dialogResult == DialogResult.Yes)
            {
                cmd = new OleDbCommand("update Medicine_Available_Detail set [total_available]=total_available-1 where [Medicine_Name]=@Medicine_Name", con);
                //cmd.Parameters.AddWithValue("@total_available", medicineavailable);
                cmd.Parameters.AddWithValue("@Medicine_Name", medicinename);
                con.Open();
                int n = cmd.ExecuteNonQuery();
                con.Close();
                MessageBox.Show("Record Updated Successfully");
                showdata();
                dataGridView1.Refresh();



            }