You can get this cable extension kit for 3 pin ARGB: https://www.amazon.com/MICRO-CONNECTORS-3-Pin-Addressable-Extension/dp/B07YYZD18R but that is only if we are talking about the newer ARGB version. If you have a older 12V RGB fan then you use this one instead: https://www.amazon.com/Micro-Connectors-F04-RGB01-30-Extension-Cable/dp/B07GN1C5L5/

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What controler are you using?