This refrigerator uses a static cooling system where the back wall of the fridge is the cooling apparatus and accumulates frost. Do not worry it automatically defrosts itself and requires no maintenance.
The static cooling system on this refrigerator has an evaporator integrated into the back wall. As such the back wall gets cold (below freezing) and the moisture in the air will naturally freeze when it contacts the back wall. This is completely normal and requires no action by you. Periodically the fridge will defrost the back wall and the water will drip into a small hole at the bottom of the fridge on the back wall. From there the water will run into an evaporation tray on top of the compressor and will naturally evaporate back into the environment when the compressor turns on and heats up.