Stuck at "Bring External Data into the Contact Page Layout" of Agentblazer Champion

See "Connect Data Cloud and CRM with Enrichment" section. The instruction there says: "In the right menu, under Related List, choose Reservations".  However, Reservations are not available, only ExternalReservation. If I select it, "Add Field" button is dimmed. See the attached. I cannot do the following: 

1. Under Related List Fields, click Add Field.
2. Find and select Check-in Date.
3. Click Done.
4. Repeat steps 6-8 for Check-out Date, Room Type, and Reservation Status.

#Trailhead Challenges  #Trailhead