The Motorola G5s Plus can be identified by its model number: XT1804 (varies based on country). It is an updated version of the 5th generation of Motorola’s Moto G series. Some distinguishing features of this device are its metal unibody design, improved front and rear cameras, and bigger battery.
My g5s plus drop in the water, after that not have signal gsm, the SIM is recognized (ask the pin and shows the company name of the sim) but can't search phone networks, when I try scanning appears error network. How can know if the problem is the signal cable was disconnect or the motherboard phone?
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 IPA 90%+ (Isopropyl Alcohol, available from most pharmacies) to remove all traces of corrosion and water. Do not use "rubbing alcohol" as in some cases this is only 70% or less, may contain scents and is not as effective. If you do check the label to verify the amount
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 Moto G5s Plus Repair guide(s) for your phone which may be of some help.
If this process seems too daunting, take your phone to a reputable, professional phone repair service experienced in water damage repair and ask for a quote for a repair. If you decide to do this, do it sooner than later.