I just built my system and want to do a bit of overclocking. I have a 9700k, an ASUS Z390I, and a Noctua L9I. I wanted to do some light overclocking, but I can't find how to change the CPU fan speed in the ASUS BIOS. Thanks for all feedback.
Once you are in your Bios, F6 displays the current settings of your fans and used to manually tweak the fans to your desired settings. Your CPU fan cable should be connected to CPU_FAN header. This header has PWM control however your Heatsink cable must be a 4 pin connection to have speed control.
The Noctua L9I is totally inadequate for Overclocking (even mild OC) a 9700K and you would need to set your CHA Fans at a speed that would be rather noisy.
Run a stress test for 20mins to check your temperatures under full load to see if your system copes at stock frequency.
Normal temps are 10-15C above ambient room temperature at idle and 65-70C under full load.