You can re-use the customer list that you created previously and include it as a subworkflow.
- Select and drag
to the canvas. 
- In the Properties panel, select TUTORIAL_CUSTOMER_EVENTS, the customer list that you created earlier.
- Connect the customer list by selecting and dragging from the connector dot in the Start node to the Workflow (TUTORIAL_CUSTOMER_EVETNS) node.
The errors you’re seeing indicates that you have an incomplete customer list with no success path. You'll fix that by adding the the new data source.
- Select Save Customer List.