This won’t work with some rare fan types but its not hard to try
Common ones are the Power Supply fans and in most cases it is cheaper to replace the power supply than repair it, but when necessary, this is the procedure that I use.
It takes much longer to describe then to actually do it. Having done 100’s I can do one from start to finish in about 10 minutes
To do it, remove power cable (VERY IMPORTANT) then take out the 4 mounting screws and lift out the supply
I leave it all connected if possible to save time, and just sit it on the side of the case
Remove the power supply cover (usually 4 screws) Take out the 4 fan mounting screws and lift it out..
Lay it down with the label side up. Using a craft knife, peel the label off and try to preserve it.
Under the label is a round flexible plug. I use a sharp needle to prise this out.
I put a drop of thin oil into the well and spin the blades manually to work it in.
Refit the rubber plug, then clean around the area and also underneath the label with alcohol.
I use isopropyl alcohol as I have it here, but Methylated spirits will do.
Lastly use a light contact adhesive to re-glue the label.
If the label is damaged or missing, a piece of sellotape or even a circle of paper will do… However it is required to stop the plug working its way out
Refit the fan, the power supply cover and remount the supply.
I have done this with Power Supply, Case fans, CPU, Chipset and Graphics card fans. Graphic Card and Chipset fans are often necessary because these special fans are often impossible to source.