Upper freezer not freezing, Lower freezer working properly

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1

Please make sure to click on General above and select the correct appliance type first

Brand:
Model Number: RM255LABP/XAA
Main Symptom: the left side UPPER FREEZER compartment is NOT freezing anymore (seems to have reverted back to refrigerator status), while the LOWER SECTION of the FREEZER is still working properly.
What might be the problem and what part do I need to order?

Error Code (if any):
Parts or tests already tried:
Photos / video link:

2

Open the rear panel and check the evaporator fan motor to make sure that the fan is operating. If the fan is operating then you would check to make sure that the evaporator is not frosted over. If it is then this would be a defrost issue and would need to check the defrost thermostat, defrost thermistor, and defrost heater. If they good then this will be a faulty control board.