Your best option is to do an out of warranty replacement with Apple--turn in your phone and pay $299 for a discounted refurbished phone.
Rice is a myth, it does nothing to actually treat water damage and has the same effect as just letting your phone air dry next to a pile of rice on the counter which is a lot less messy, plus you can still cook a risotto when the phone is dry.
The ideal solution to water damage is quick treatment while the phone is still wet. You have to get the phone to a qualified repair person who is able to open the phone, take out the board, desolder the shields on the logic board and address any corrosion on the board with ultrasonic cleaning, 99% alcohol to displace the water, and then drying and replacing damaged parts as necessary. Apple can not help you with actual repair of a water damaged phone, and outside of immediate treatment while the phone is still wet---most independent repair shops can't help you either. Water damage weakens soldered joints and insults components throughout affected areas on the board and the phone will just be a lot more fragile and finicky than before. I recommend that all water damaged phones be replaced.
To answer your specific question---if you did want to put resources into fixing this particular phone, the first step is to replace the LCD display which would likely solve your display problems. Unfortunately, the 6s LCD display assembly prices for an original quality display are quite high right now. ~$200 for the part.
It would not be in your best interest to pursue independent repair of a wet 6s right now, since the overall repair price would be too close to the out of warranty swap price at Apple and you'd be left with a phone that has seen water and may develop early failures down the road.
best of luck!
jessa