iphone 5s can't activate after drop into water

My iPhone 5s drop into water, after dry for days it seem good to ON back but battery seem not working good. To be honest, I replace with not original battery to make sure there is no others problem. And becoz not easy to find original services center. Now everything is fine but cant activate the phone as system keep telling server problem. I went to apple Store to advice but they said I opened the phone so they don't accept my repair. Can I know how to repair it?

many thanks and appreciate your help.