Obviously by finding the moths and dealing with them one way or another. Just interact with every purple thing in every room, and if there is something that does not work the first time, maybe you have to come back to it.
Seriously, that get's asked on the discord a lot. Have people never played rpgs before? This one is rather easy, you literally get highlights on every interactable object. You do not even have to press a key, like in some point&click games.