After integrating both accounts, you will need to review your inventory to assign each part to the marketplace of choice. This will allow you to retrieve your current inventory from the Listing module.
The step above will tell apart this inventory part as an inventory for sale. Next, you can pull the part from your inventory in the Listings module.
You can also create new listings for items not being pulled from your current inventory. A typical example is issuing a listing for items pending to be received.
Each record can be edited before being pushed to Marketplaces.