as already mentioned, without strong knowledge in electricity & electronic, I would advice you to not even try because of real danger during reparation and after.
Now I see maybe one exception for this rule: if it is only a fan related issue. If it is just your fan that stopped turning but your psu still work, replacing the fan is imho feasible.
I have encounter the problem where the fan stopped working but gpu still fed. I used an external fan controller to which I connected the fan and this psu is still functioning right now.
but tbh if I could I would have bought another psu. for the moment all is good and I hope it will still be ok