Pretty simple.Hit the three lights under the cube in the top center then it will rotate, hit it again and it will lower. After that shoot your ball into the cube and that's it.
**Note**
Thanks to TerreBullet for bringing this to my attention. On the Red Skull/Baron Zemo missions it will take 2 hits after the rotation to expose the cube.
I have also found that on the Cap missions it will only take one extra hit to expose the cube.