If there is normal (about 0°F to 5°F) temperature in the freezer but the refrigerator is warm then most likely the air diffuser is bad and has to be replaced.
You can find the complete removal and installation instructions for air diffuser in this
Service manual.
Hopefully this post
Control Box Removal will help you to find the way on how to remove the control box.
- The part number for the air diffuser is
AP3046080
Gene.