How to fix my water damaged Samsung Galaxy s3?

My friend dropped her Samsung Galaxy s3 in the bath tub and it stopped working. She put it into rice for a week or two but got a new phone before even checking her broken one. So I offered to take it and maybe try to fix it up so I could use it. The LED lights and sound work but it s just the screen. When we first put it on again for the first time in days(which was yesterday), we heard all the notification sounds and the vibration of the powering up but we couldn t see what was going on. The screen was complete black. It ll pop up a static greenish color, like on TVs sometimes and the buttons and led lights would light up and the phone would vibrate but the screen was the only problem. Putting it into rice won t help and I ve tried unscrewing the back but there s no mini screwdriver available. Is there anything I could do to fix it besides bringing it to someone?

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