DIAGNOSIS This is almost always caused by a clogged or frozen defrost drain. These fridges have a small drain hole at the back of the interior, usually under the bottom shelf. When it clogs, defrost water from the freezer section can't drain to the evaporation pan and overflows into the fridge compartment.
FIX 1) Unplug the fridge and remove all food and the crisper drawers. 2) Look for a small hole in the back wall, near the bottom. You'll likely see ice or gunk blocking it. 3) Use a turkey baster filled with warm (not hot) water to gently flush the hole. A pipe cleaner or flexible straw can also help clear the clog. 4) Pour a little warm water into the drain to confirm it flows freely to the drip pan underneath the fridge at the back.
IF THAT DIDN'T WORK If the drain is clear but water returns quickly, the drain tube itself (which runs from the hole to the pan) might be kinked or disconnected inside the cabinet. That requires more disassembly to access.
HEADS UP Prevent future clogs by making sure food packaging isn't blocking the back wall where cold air flows, and don't set the thermostat excessively cold. A too-cold setting causes more frequent frost cycles and more water to drain.