Replace the thermostat.
I used the instruction video on the web site. It is easy to dissemble it. However to reassemble it took some trial-errors. When I reassemble it, then I realized that I don't need to unscrew every the screws. You would have to line up components to put screws back on. You will need to line up the freezer temperature control with the lever that connects to an opening of the freezer. It took me 4 tries to reassemble but overall it is not a difficult job.