Why is it overheating and shutting down?

Hi

As you know water and electronics and electricity are not a good mix.

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 is ongoing until it has been properly cleaned away

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 LG Tribute HD repair 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.