Hi Huy Phạm1
I am Dave, I will help you with this.
That fan error is a known bug on Dell laptops, the Dell forums are full of people reporting the same bug and usually that does not mean there is anything wrong with the processor fan on your laptop, it is a false positive, if you run the Dell Diagnostics again, does it still report the same error?
Do you hear the fans on your laptop working when you are doing an intensive task?
Does your laptop overheat or become very hot if you do nto hear the fans?