How do you fix my dsi camera?

In what way are they broken? If none of them work, surely it means the DSi is At Fault.

Test the games on someone else's DSi. If they work, then you might need to send your DSi off for repairs. If none of them work, you can try sending those too, but if the whole lot have stopped working, it sounds like damage through neglect or an accident, none of which is really fixable by a non-specialist.