How to save iPhone after putting it in rice to prevent water damage?

@gigabit87898's advice is good but at this point, your only option is to have it looked at by a professional repair shop. The damage has already been done by letting it sit in rice for so long. A repair shop will do a proper decontamination and troubleshoot the board. Some shops don' t like to fix the phone for the sake of the phone and focus only on data recovery. IMO, phones that have limited and localized damage are usually salvageable. That said, the only way to know is to strip the logic board of its shields, inspect and clean in an ultrasonic bath...and then troubleshoot.