Fridge freezing up anf not cold

model #10651133210 kenmore refrigerator forced defrost mode

is there a forced defrost mode for this fridge. it looks like snow on the back wall of freezer. i unplugged it a couple days then plugged back in and it worked fine for 3 days. now snow forming again and temps are slowly going up. any idea what part i would need ty

it could maybe possibly be thermmostat. define possibilitty