How can I deselect the bomb in "Keep Talking..." on Samsung Gear VR?

I have a Samsung Gear VR and downloaded "Keep Talking and Nobody Explodes" but have been unable to pass the tutorial. The tutorial instructs you to "deselect" the bomb to place it back down on the table. The accompanying diagram highlights a button just above the touchpad on the headset. On my headset, the two buttons in this place are the "Home" and "Back" buttons. The home button prompts me to quit the game, whilst the back button does nothing. (I have tried holding the back button as well as short-pressing it). Perhaps I am missing something obvious?