If the model number is RF267AERS/XAA, do this.
Press the Energy Saver button and the Fridge/Power Cool button at the same time for 8 - 12 seconds. Once the display changes to FF 1, you are now in forced freeze mode high speed. Press the Power Freeze button once and it will go to FF 2 forced mid speed run. Press the Power Freeze button again and it goes to FF 3 forced low speed run. Press the Power Freeze button again and it will go into Force Defrost. Forced defrost will not work if the bi metal sensor is bad. You will have to use a steamer or hair dryer to clear out the ice.
Hope this helps.