Yeah but how do I find the UPC product id of that product?When you add a product, you enter a upc which is the barcode number, if the product exists on amazon already you will see the product details. The asin is a number issued by Amazon to every product. If you are selling an existing Amazon product it will already have an asin you can't change this.
If you are adding a new product to Amazon with a upc that is not on Amazon already Amazon will give the product an asin after you create it.
Does that make more sense?