If it's open, the fault is going to be a blockage in the ducting between the freezer and fridge or, a blocked evaporator in the freezer.
First, unplug the appliance.
Take the rear panels inside the freezer off to expose the evaporator.
if the evaporator is a solid block of ice, fully defrost and then reassemble to try the machine again.
If it's all clear, it's a blockage in the ducting.
To cure this, you have to carry out a full defrost of the appliance.
At least, 24 hours unplugged, doors open and in a warm room.
After this, close the doors, turn it on and it should cool down again.
Check it out, see what you find.
Hope this helps
Let me know how it goes