Behind the back freezer wall is the evaporator ( cooling coil ) . Periodically the defrost timer will energize the defrost heater which is right above this vent you're referrring to. If all the food in fresh food and freezer are maintaining their correct temperature I am going to assume that you just happened to catch the refrigerator in defrost. When this ice melts it should go into a trough at the back wall and then into a tube that ends in a pan under the fridge, if you have water coming out the freezer floor then this drain and or trough is clogged and frozen.
You have to get to the hole in trough to defrost it and get the tube unclogged. Do this from inside the freezer , remove shelves and the back wall and use a hair dryer and a turkey baster with hot water to push hot water down in to the hole . Eventually it will open and the water will go down into the pan underneath . Unplug the fridge when you do this. It takes up to an hour so your frozen food will be ok for that time period setting out. Thanks for using justanswer.
P.S. Dust on coil has nothing to do with this problem and there is nothing to reset.