Works on atmosphere but didn't tested on ReiNX and SX OS.

I'm giving the needed file, copy this to atmosphere>config folder in sd card. DON'T FORGET TO CHANGE THE EXTENSION OF FILE TO .ini OR IT WILL NOT WORK I already modified and bumped the speed level by one tier in every section (except first temps., no need to wear fan on room temp.) for less temperature. Modify if you need.

Default settings are these:

Code: 
[tc]
tskin_rate_table_console = str!"[[-1000000, 40000, 0, 0], [36000, 43000, 51, 51], [43000, 53000, 51, 153], [53000, 58000, 153, 255], [58000, 1000000, 255, 255]]"
tskin_rate_table_handheld = str!"[[-1000000, 40000, 0, 0], [36000, 43000, 51, 51], [43000, 48000, 51, 102], [48000, 53000, 102, 153], [53000, 1000000, 153, 153], [48000, 1000000, 153, 153]]"

str!"[[-1000000, 40000, 255, 255]
-1000000, 40000 these are temperature 40000 = 40C
255 is the speed, 0-255

Edit: lesser fan speed maybe would NOT work, for built in security. Even if they work, BE CAREFUL YOU CAN OVERHEAT AND DAMAGE YOUR CONSOLE!