The first result on my search engine is the Blendermarket page https://blendermarket.com/products/k-cycles which clearly states it is a custom build, not an addon.
There’s a Discord server too, I suppose you can use that to contact the author directly for help. But I’d be surprised he didn’t bundle a readme/instructions with the download.
Here’s his thread for announcements and support : K-Cycles - 4.0 Performance Update, New Light Mixing Ultra Lighting, Post FX, & Denoising
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