If the fan still works,give it a good cleaning then at the bottom there is a label,use a small blade to prise it open carefully.
There might be a small rubber plug covering the bearing hole,get some engine oil(just a tiny drop will do)in there.
If you don't have engine oil,3 in 1 or WD40 will do but they won't last that long and as good.
(wipe off any surplus)
I have done this many times before to Mobo with this kind of chipset fan design and usually it'll give me 1-2 years troublefree and noisefree service.(with engine oil)