Struggling to do airflow simulation on project

Hello, I’m a first timer to this software and forums. I’ve watched some webinars but i’m still a bit confused.

Im looking to run some airflow simulation on my project. I’ve imported the model and created a mesh but Im not sure how to select the input for the airflow and the output. Its asking me to select “faces” but im not sure which face to select since my geometry is hollow rather than solid.

Here is my project SimScale

Looks like good candidate for ‘Flow Volume Extraction’.