Spawn as either Class-D or as a Scientist. Inside Light Containment you will find SCP-914's Containment Chamber, marked as 914 above the doorway. Any keycard will open it.
Place the keycard inside of the leftwards room of 914, and activate the machine on the setting "Fine." Pick up the card on the opposite end of 914 when it opens and repeat several times until you get the black and white O5 card.
There are guides to exactly what each setting will do, but typically 'Fine' will bring your keycard to an O5 after 914's activation 3-4 times.