Control 3-pin fan speed on 4-pin header

I have a ASRock H170M Pro4 motherboard and my chassis fans are two Fractal Design Dynamic GP-14 (which have 3 pins). Does anybody know how to prevent them to always run at full speed? I searched a lot on the net and found no solution at all. ASRock claims that 3-pin fan are adjustable even if connected to 4-pin headers, but in BIOS I couldn't find anything that could help me to sort this out.