I sympathize! The manual for that mobo shows virtually NO details of what the configuration options are for its fan headers.
Concentrate on the CPU_FAN header, for that is the one to which you connect your rad fans for power and control. There are three options for you to adjust.
1. Options for PWM Mode or Voltage Control Mode (aka DC Mode) - set to PWM Mode for these 4-pin fans.
2. Options for Fan Profile usually include (a) "Automatic", "Normal" or "Standard"; (b) "Manual" or "Custom"; (c) "Silent" or "Quiet"; (d) "Turbo" or "Full Speed". FIRST look at what the graphical display of fan speed versus Temperature shows as the "fan curve" it is already using.
3. Now set to use the "Manual" or "Custom" option. Then adjust the circles on that graph for your new choices - as I said, mainly move the circle close to where the fan is already operating, and just move it sideways to change the Temperature at which it will change speeds. That video linked above by UsandThem will help to understand.
When you have all your changes made, use Esc to get back to Main Menu, then F10 to get to the Exit Menu. There use the SAVE Changes and EXIT to reboot with the new settings.