You cannot control the speed of fans connected to a motherboard header with Corsair Link. You'll need to set this in your BIOS or with any software that your motherboard manufacturer provides.
You didn't mention the motherboard manufacturer either so it's hard to provide specific guidance. With Asus motherboards, the AIO_PUMP header is simply a standard fan header with Q-Fan control disabled by default. If you go into Advanced settings in the BIOS, you can enable Q-Fan control on that header and then set a fan curve. If you have another manufacturer ... dunno.