Variations in Amazon don’t normally display the individual ASIN’s for the product. To get the variations ASIN you need to go to the product page on Amazon. Add each variation you need the ASIN for to your basket. Once you have them all added go into your basket and you’ll see each variation of the product listed.
Right click on each product and select to open in new tab, this will open up each of the product variations own pages, you’ll notice when you open each they will open to the correct variation. In the website URL the ASIN for each product is listed, you’ll notice that each are very similar to each other with only a slight difference, take this ASIN and use it to add your own variations to SellerExpress.