How to select a specific row of a listview in C# WPF?(Not selected row.)

Question

I am making a point of sale program which has basically a listview and product entrance. When the person enter the same product, this program should increase the quantity of the existing product on the list, not creating a new whole row.

So, my question is that how to dynamically add items in ListView in WPF. I mean, I would like to choose a specific row of a listview to get a specific cell on it. But I don't want to get the selected row. Just a specific row.

Let me describe it as a matrix: lvProduct[0][2]. This should give me second cell of the first row. How to apply it in C# WPF?

My code is as follows:

    private void btnProductAdd_Click(object sender, RoutedEventArgs e)
    {
        bool addNewProductLine = true;
        decimal totalSalePrice = Convert.ToDecimal(txtProductPrice.Text) * Convert.ToInt32(txtProductAmount.Text);



        for (int i = 0; i < lvProducts.Items.Count; i++)
        {
            ProductBLL product = lvProducts.Items.GetItemAt(i) as ProductBLL;

            if (product.BarcodeRetail== txtProductBarcode.Text)//If there is already the same item on the list, then confirm to add them together or not.
            {
                if (MessageBox.Show("There is already the same item in the list. Would you like to sum them?", "Confirmation", MessageBoxButton.YesNo) == MessageBoxResult.Yes)
                {
                    product.Amount +=Convert.ToInt32(txtProductAmount.Text);
                    addNewProductLine = false;
                    break;
                }
            }
        }

        List<ProductBLL> items = new List<ProductBLL>();
        items.Add(new ProductBLL() { BarcodeRetail=txtProductBarcode.Text, Name = txtProductName.Text, UnitRetail = Convert.ToInt32(cboProductUnit.SelectedIndex), SalePrice = Convert.ToDecimal(txtProductPrice.Text), Amount = Convert.ToInt32(txtProductAmount.Text), TotalSalePrice =  totalSalePrice});
        //lvProducts.ItemsSource = items; This code renew the listview completely. That means, it erases old datas and writes the new ones.

        if (addNewProductLine == true)
        {
            lvProducts.Items.Add(items);
        }

        ClearProductEntranceTextBox();

        //items[0].BarcodeRetail = "EXAMPLECODE"; This code can change the 0th row's data on the column called BarcodeRetail.
    }

Unfortunatelly this code does not work :/

Thank in advance everyone!