By default, whenever you add a store / marketplace to ShipStation, it'll automatically show up with your other stores and marketplaces (refer to screen below).

However SellerChamp will not be visible, as it is working in the background.

Within your SellerChamp Integrate with ShipStation page, as long as the button to Disable Integration is visible (refer to image below) your SellerChamp account is integrated with ShipStation successfully.