In the Importing CSV Data into Neo4j > Using the Neo4j Data Importer > Importing CSV files with the Neo4j Data Importer exercise, there's a typo in the steps that could throw people off:
Step 7: Define the DIRECTED relationships mapping > 2. In the Mapping Details pane on the right: > c. In the IDs section: > i. Select tmdbId as the Person ID.
Should read "Select person_tmdbId as the Person ID." since the mapping seems to follow the CSV headers rather than the renamed property associated with the node.