Press and hold, then swipe up and hold with one finger to put the crate on top of you, then swipe up with another finger (while still holding with the first one) to throw.
This is not obvious, as you can easily play the entire game except this part with just one finger.
So if you got to that point, it means you already got all the orbs. I'm assuming, though, that given your question you don't really know where to get the code from, and only got it from the guides. So let's go back a bit.
Remember how to get orb #5? After you go down the stairs, you'll notice some sounds start to play in the background. Now, one might ...
The ending (and the title) of Inside suggests that the boy you thought you were playing as all along was really being mind controlled by the real player-character: the blob. The game sets up a few hints along the way:
When you're plugged into one of the mind control "helmets", you can control somebody else. The blob has several of the mind control machines ...
L3 and R3 are not used in the game.
The screen shot below is the controls page from the in game options menu, taken on my PS4.
The controls are simple:
Left analogue Stick to move
X to jump
☐ to grab / interact
If you look closely in the scene, the boy actually drowns. Then, just a bit later, you'll also notice something gets attached to him — when playing through this the first time, I assumed that whatever got attached to him somehow gave him the ability to breathe under water (in fact, I was pressing the action button all the time, and thought I'd saved the boy, ...