display is not bright after it fell in water

How thoroughly did you dry the phone? You should turn it off immediately, remove the battery and place it in a jar of dessicant (silica gel or uncooked rice) for a couple of days. Hair dryers etc are not recommended.

To be honest, it's hard to say what to do with a water damaged phone. It depends on what has been corroded. It might be that replacing the display will fix it, or it might be that the connectors on the motherboard are shot. And if you do replace the display and it works, it's possible that something else will fail days, weeks or months later. Water damage is like that - you might be lucky, but there can be no promises.