Fridge icing up on back wall

Hi there recently moved into my first place and have noticed my fridge (second hand) has droplets of water that have frozen on the back. Does anyone have any idea why this might be? I suspect I may have the temperature set too high potentially, I have put it on 3 (out of 6). Have googled it and it says a load of other potential issues but I don’t really understand them! It’s an under counter fridge with a small freezer compartment at the top!