Are you prepared to take the cover off and examine the internal workings?
Assuming you are, then the freezer will be controlled by a thermostat. When the internal temperature is too high, then the compressor should run.
So put the freezer in the normal operating mode, and see what happens. What should happen is that the compressor should start running, and maybe a circulation fan should also be running. When the compressor is running, the evaporator coils should get freezing cold.
Check if any of these things are not happening, and then work back from there based on what you observe.
For example, if the compressor doesn't run, then check the operation of the thermostat, or any relays that control the compressor.