Why does my self defrost fridge freezer ice up in the freezer section?

Have a Samsung Fridge Freezer model number RL365BSVV. It is a self defrost, water has been draining and icing up the bottom of the freezer section. We have had the engineer out three times and all he does is take the back out and chip the ice away. Then within days the ice is back. We live in Spain and to get an engineer out is impossible. My husband could do this himself with guidance, can you help please?