Try drying out the water usually by putting it a bowl or bag of dry rice, hopefully that will work and no damage will have been done to your phone. Otherwise things get a bit more complicated, whether you repair it yourself or go to a shop the cost of repair will depend on what has been damaged; pray it isn't the logic board. My advice is if you can turn it on try to assess the damage and make the respective repairs if any, if you can't turn it on, bring it to a certified repairman.