You can only find this free battlestar after unlocking the Opening Night Loading Screen.
This is the Opening Night Loading Screen for reference:
You can see the characters watching a movie at a drive-in theater.
If you look closely on the back of the red pickup truck, you will see a transparent battlestar.
The drive-in theatre is Risky Reels.
There is a red pick-up truck close to the movie screen. (in first line of cars from the front)
The battlestar can be found on that truck.
See screenshots and maps below to help find the location of the secret tier.
- You can only locate the secret battlestar after you have unlocked the Opening Night Loading Screen.