It's a big question - How can I fix it?
You give little information about the make and model or the precise nature of the fault - or anything you might have done so far.
You do not mention your skill level and experience of repairing things like this.
It would be flippant to advise you what tools to buy and courses to attend - so your best approach may well be to have a specialist look at it - a friend who has skills and confidence or a professional - yellow pages for the area where you live.
Good luck...
December 2014