A recent episode of Re: Zero is titled 地獄なら知っている, when I watched the preview I could not understand exactly what it meant but when I finally saw the translation, they translated it as "I know hell" but the literal translation is as far as I know: "If hell, I know". Furthermore, in the context of the episode, the main character says the phrase "地獄なら知っている" in order to indicate that he has been through hell/knows what suffering is.
How does the なら particle work in this scenario?
Thanks