Fans can't be controlled by software with a 2 pin connector. If you have a fan controller, you can plug it in there and it will undervolt it causing it to become slower. Other than that, even if you were able to find the adaptor, it would not be able to be controlled through the OS. Suggestions? Well, other than having a pointless fan controller and cables going everywhere, I can't think of anything else.
See the thing is i have done that. I bought an akasa fan speed controller but they only take standard case fan 3 pin and not gpu 3 pin