As you already are aware, that in order to list any item(s) on your marketplace using SellerChamp, you'll always add them to your SellerChamp marketplace manifest first. Then, you'll submit the manifest. Simple.
Similarly, whether items are automatically imported (using Auto-Import inventory option within the integration settings) or manually imported (using the Import Now option), they all will be collected into a manifest within your destination marketplace, Channel Imports folder (refer to image below).
Items will remain within the destination SellerChamp marketplace manifest.
Submission of the items, within the destination SellerChamp marketplace manifest, will depend on whether you have the Auto-list after import option turned on or off (refer to image below).