As you know water and electronics and electricity are not a good mix.
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.
First do not turn on your phone and then you need to with the phone turned off, remove the battery as soon as possible from the phone to minimize further damage.''
Then you need to dis-assemble the rest of the phone and clean all the affected parts using Isopropyl Alcohol 90%+ to remove all traces of corrosion and water. Do not use "rubbing alcohol" as in some cases this is only 70% and is not as effective. If you do check the label to verify the amount
Here is a link that describes the process.
Electronics Water Damage
You may have to replace the battery as it is very hard to recover a battery from 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 is a link to the Ifixit guide for replacing the screen in your phone. It is handy because it shows how to dis-assemble the phone.
Samsung galaxy s5 neo Display Replacement
If this process seems too daunting, take your phone to a reputable, professional mobile phone repair service and ask for a quote for a repair. If you decide to do this, do it sooner than later.