Aye, you can turn the unit off, but most likely the frost will come back if you have a bad defrost component. Perhaps a diagram will help, but you need to remove part 214 in the diagram in the link below.CLICK HERE
You'll need to either unplug the unit for 24 hours or remove everything of the freezer and remove the lower back panel inside the freezer to defrost it with a hair dryer. Once all the frost is thawed out, the unit will start working again. To make sure the problem doesn't come back, you'll want to replace the defrost heater. GE's defrost heaters fail often because they are nothing more than a long glass light bulb. Order and replace the defrost heater at the bottom of all the frost and you should be good to go. Below is a link to the defrost heater you'll want to order and replace.CLICK HERE
Now I did want to point out that there are a few other possibilities like the defrost timer/control board or the defrost sensor, but these rarely fail on this model and there is no way to test the heater for certain to know if it's good or not. The reason is because that the heater is glass and can get water inside of it when it fails so it will show good continuity even when it's bad sometimes. That's why the best course of action is to replace the heater since it's by far the most common problem. Also, if you happen to remove the back panel and the coils aren't packed with frost, then that would mean the fan above the coils is likely not running which will generate the same symptoms. You'll need to order and replace the evaporator fan motor if this is the case.
If you really wanted to test the the sensor, look for the white plastic bullet at the top of the silver evaporator coils
with 2 small wires going to it. You'd need to cut the wires going to the sensor and then put the sensor in ice water for 5 minutes. The resistance should be right around 16.3 kΩ. If not then the sensor would need to be replaced. I don't advise doing this test because you must cut the wires just to test it so I'd reserve this option in case the problem persists after you replace the heater.