I have a Bitfenix Enso case and at the back there is 2 rgb cables one for the fan and one for the front of the case. The front rgb cable has only 3 holes instead of 4. So I can’t plug it into the 4 pin rgb header on my mobo.
You can plug it into the 4 pin RGB header, it will be perfectly fine. The 3 pin fan has no PWM (pulse width modulation) control, which is what the 4th pin is for.