Given - You have one fan header and three fans.
solution
cheap and basic - two of these
https://www.newegg.com/Product/Product.aspx?Item=N82E16812423172
More expensive solution (better solution)
https://www.newegg.com/Product/Product.aspx?Item=1W7-0053-00005
High end solution
https://www.newegg.com/Product/Product.aspx?Item=9SIA9ZH3TU3787
Thank you for the solutions. I probably will go with the cheaper option, but just out of curiosity, how does the power cable splitter work? Again, sorry for the questions, I just want to learn more about this matter.
I hope that helps. the fans plug into those for power, there are such a thing as fan splitter cables, but they are not recommended at all.