You can target specific products with your message using the item filters. You can also exclude specific products from receiving your message. However, you should keep in mind that you can only enter ASINs or SKUs into one of the Item Filter fields for each message.
For example, you cannot enter ASIN123 into the "ASIN is" field and ASIN456 in the "ASIN is Not" field. If you wish to use one item field over another, please delete the ASIN(s) entered in the first field, and then you can update the desired item filter field. The same applies for SKUs.