An IP68 rating is not a waterproof rating. It is a water resistance rating i.e immersion in up to 1.5 metres of water for 30 minutes maximum. This doesn’t take into account the state of the phone at the time that it is immersed, e.g slight cracks in the case, or case slightly bent perhaps etc. who knows but something happened that allowed the water to get in.
The phone will have to be opened and properly cleaned of all the corrosion that is still occurring in the phone due to the water interacting with the metals and the power in the phone. The corrosion is most likely the cause of your problems
The impurities in the water causes corrosion and provides circuit paths for the electricity which were not in the phone's operating design and could damage the components. The corrosion starts immediately and is ongoing until it has been properly cleaned away
Rice does not fix the problems caused by the corrosion occurring in the phone
Rice is for dinner, not repair
First do not turn on your phone and then you need to remove the battery as soon as possible from the phone to minimize any further damage.
Then you need to dis-assemble the rest of the phone and clean all the affected parts using Isopropyl Alcohol 99%+ (available at electronics parts stores) to remove all traces of corrosion etc. Do not use "rubbing alcohol" as in some cases this is only 70% IPA or less, can contain additives and is not as effective. If you do check the label to verify the amount of IPA. The higher the percentage of IPA the better.
Here is a link that describes the process.
Electronics Water Damage
As always with electronics, especially surface mounted PCBs be gentle when handling and especially when brushing away the corrosion. You do not want to remove any components from the board.
Hopefully after you have done all this the phone might possibly work correctly again.
Here’s a link to the ifixit Samsung Galaxy A5 (2017) guides which may be of some help.
If this process seems too daunting, take your phone to a reputable, professional phone repair service, experienced in liquid damage repair and ask for a quote for a repair. If you decide to do this, do it sooner than later.