If you already have an active account on Seller Central with products uploaded from a different platform or module, you can keep you synchronization active and avoid creating duplicates. In order to achieve this, AmazonSync must use the same SKU your products currently on sale have on Amazon.
You can select the SKU source within the module’s General tab: the possible values are reference, EAN o supplier reference.
Should your Prestashop products be missing the EAN code, then you can perform an inventory download to automatically associate ASINs. After this, go to the Sync tab and enable Prioritize ASIN code to let those listings be exported.