Hey there bud.
By big hologram, I assume you meant the final boss. (MZARK-AI2)
Here's how.
1: Go to the pedestal where you placed the cubes before, and interact.
2: A maze will spawn.
3: Make your way through the maze, (or no-clip if your lazy.)
4:Find the pedestal, and remove the cube.
6: Repeat this two or three more times, I forget which.
7: Then, you can attack the big hologram.
Cheers!