You can convert an FBM SKU to an FBA SKU through your catalog on a per SKU basis or in bulk (see below). A few things to note - If you change a SKU in seller central to FBA but not in Zentail, and you have product data sync enabled, Zentail will change your SKU back to FBM. After changing the SKU in Zentail, please allow at least 30minutes for it to update in your seller central.