How do you change the word dark to a noun?

You can't directly change "dark" into a noun. However, you can use it as a noun in a few ways:

* Use it as an adjective to modify a noun: "The dark of the night"

* Use it as a synonym for a noun: "The darkness engulfed the room."

* Use it as a part of a compound noun: "The darkroom was filled with chemicals."

Let me know if you'd like more examples or want to explore other ways to use "dark" in a sentence!