Unfortunately we don't have a direct integration with Amazon or eBay. You would either have to export the items and bulk upload them onto Amazon or add each product manually. We have information on how that could possibly work here: https://intercom.help/modalyst/modalyst-for-retailers/tutorials/how-do-i-add-products-if-im-not-using-bigcommerce-or-shopify

Since we don't support Amazon directly, you would need to find out how to list those products based on the requirements set by those them (such as UPC codes or GTIN numbers). If they have this information available, they would be happy to share it!