If you are using Patchwork Devices and want to transpose, try adding a Note Progressor. This tutorial sets you up with a basic build using the Note Progressor. There is also a video that covers some music theory (what transposition is), a catalogued version of the chord progression presets, and a play through of said presets (but played live on a piano).
https://dev.epicgames.com/community/learning/tutorials/LJP9/fortnite-note-progressor-basics-transposing-with-patchwork-devices
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