The heater is mounted at the bottom of the evaporator, and is usually held in place with metal clips/brackets. However, due to the process needed to install that heater, which I believe is going to look like an "L", you have to pull the bottom of the evaporator away from the wall. I would HIGHLY RECOMMEND you dont try this yourself, because without proper training, you can damage part of the evaporator coil by bending it, in a way similar to kinking your garden hose, and if you do that, that is a MAJOR repair, and VERY expensive. I would seriously consider calling a local refrigerator repair company and have them install that for you.