First thing is that you must have a professional seller account – the integration isn’t allowed on individual one.  And as Shopify no longer supports the native integration (where you could simply add Amazon as another sales channel in the Admin settings), you need to look for a Shopify Amazon integration app. There are several of those in the Shopify app store, so you’ll have plenty of solutions to pick from. Or if you don’t even know which to choose, you can ask our development team for help