ASINs, which are 10-character unique product codes, make it possible for both buyers and sellers to look up and recognize particular goods.
These codes may contain both letters and numbers. The ASIN of a product can be found on its Amazon product information page.
You have the option of using an existing ASIN or creating a new one when listing a product on Amazon.
You can add ASIN only in this case when you’re creating new listing, for this you can go to add a product and then select a category and list your product then amazon automatically provides you the ASIN.