To get the center cover off, remove the shelves first, then pry the lower right and left edges of the center escutcheon until it snaps off, working your way upward. Inside this cover is a damper and a 5 volt DC fan motor for the FF side. This whole piece comes as a kit, damper, motor and all. Did one last week.
Your freezer should have gotten down to 0 within 22 hours. You also have sealed system issues. Describe the frost pattern on the evaporator coil.