Greetings, I would highly suggest to look at the manuals with these products, there are wiring guides and layouts of where everything will plug into. If you don't have the physical copies you can get them from the manufacturer's website such as https://www.asus.com/us/Motherboards-Components/Motherboards/TUF-Gaming/TUF-GAMING-B550-PLUS/
If you are still having issues with this, you can upload pictures here of what cables you are referring to and we may be able to assist further.
You can get a fan splitter like this: https://www.microcenter.com/product/610177/micro-connectors-1-to-3-pwm-sleeved-fan-splitter-cable-100-mm-(394-inches)-between-each-fan-connector-black
Fan hub would also work, but it's unnecessary. 120MM fans draw about 300mA. The fan headers handle about 1A. So stick to 3 fans per header. With a fan hub, they're generally powered directly from the PSU.
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