If you want to list your inventory in InventoryLab but complete your shipment and box content details in Seller Central, follow these steps to push your batch information into a Seller Central workflow.
Once you create your batch, you can move to the Box It stage. From here:
Navigate to Seller Central and click Send to Amazon under the Shipments menu.
This should take you to your current workflow under Send to Amazon step 1b. The workflow name will match your batch name.
If you need to navigate to an older workflow, click "Active Workflows" in the top right.
Click the workflow that matches your batch name.
From here, you can close your batch in InventoryLab and move forward with completing your box contents and shipments in Seller Central.