The only way to fix (or even trying) is to disassemble it and check the headphone jack and the surrounding area - if both ar on at the same time and apple said that there is a fluid damage - the you have to look at the headphone jack first.
but be careful - this device is tiny and could be very problematic to handle
the teardown is [guide|1157|here]
use rubbing alcohol and a soft paintbrush to clean the logicboard, the connectors and the headphone jack, remove the kapton tape before you clean the parts with alcohol, let it dry and then reattach the kapton tape on the parts.
try if it works correctly - if not, look closer for any damages the water could have made