If you already have created a Punch Out order and exported it to Astore Shop you cannot increase the number of products unit directly in Astore Shop.
If you want to add a product to your cart or order more units of a product that is already in your Punch out cart, you need to go to the supplier Punch Out website again and select the products you want to add to your cart.
Once you have selected the products you can export your cart to Astore Shop and it will automatically update your cart with the added products.
You can then finalise your order and validate it.