It is not unusual to have a thin layer of frost on the back wall of your appliance. If the wall is densely covered in ice, please see if one of the following will solve the problem.
Check the temperature setting
Your refrigerator’s temperature control may be set to an incorrect setting. Locate the dial by consulting your manual. If you’re having trouble finding your manual, download it here using your product’s model number.
Turn the dial clockwise and set the temperature. The recommended temperature is around 4 °C to 5 °C for the refrigerator and around -18 °C for the freezer compartment.
Avoid opening the door too frequently or keeping it open for long
Frost builds up primarily due to the interaction from letting warm air into the fridge freezer. To avoid this, try not to open the door too often, and don’t leave the doors open for very long.
Check the door seals for gaps, cracks, or tears
The cold air inside your appliance needs to be properly isolated from the outside temperature. Check to see if there are gaps between the door seal and the cabinet. If you find any, adjust the door seal by gently pulling away from the door using your fingers. For any openings that persist, you may need to replace the seal. In that case, contact an authorised service agent.