When you make an EntityRef on a script, dot big bang does some magic that will let you pick which entity you want to reference from the Entity menu, from a list of all the entities in your world right now.

- With Chest-Lid selected, open the Entity menu, and go to the Script section.
- Scroll down until you see Chest Lid Ref, which corresponds to the chestLidRef variable you made in the last step.
- Click the ⋯ icon to open the Select an Entity menu.
- Select Chest-Top and click the Select button.