Iphone 6s keeps restarting by itself?!

So I dropped my 6s into the toilet last week and it had a normal case on it, not waterproof, and Iquickly qiped it and dried it and it was fine for a couple of days. And then a few days later it didnt play any sound so I left it alone and then it was normal again. And just today it randomaly kept restarting by itself. Sometimes the apple logo popped up and then other times the charger and lightning bolt popped up. So I kept trying to use my phone as normal but itd turn off almost immediately. And so finally I plugged my phone into its charger and now its working fine. Any ideas on what I can do?! And this is probably a rumor but I heard that if you brought your phone into the apple store then they'd fix it for you for free if theres something wrong with the hardware. Is this true? Thankks in advance guys

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