On the picture you sent, the air flow should be at the maximum for the refrigerator. If you move the white disc that's currently sitting on the stopper manually to the right (away from the stopper), the air flow will decrease. Do that while you hold the door light switch otherwise the fan won't work and there won't be any air flow to feel in the outlet.
The bulb can't be adjusted further but if the air flow drops as the temp inside the refrigerator gets colder (but still not cold enough). You can block it open so it remains in the position it's in all the time. If that doesn't make the refrigerator section colder, you know there's something else that's wrong!
Monitor the temperatures in the freezer, it should remain close to 0°F most of the time (it will be warmer after the defrost periods).
Of course, many other things can be wrong, the defrost system needs to work fine and the refrigerating system also needs to work fine. These refrigerators defrost twice a day, when it happens, you can hear a click and the compressor stops. After that, you can hear cracking sounds from the ice thawing on the evaporator. If you look with a flashlight through the inlet grilles at the bottom of the freezer, you can probably see the evaporator fins with frost on them. When it defrosts, the ice should them and you should see the shiny metal fins before the compressor restarts and the fins get frosty again. That means the freezer is defrosting.
Removing the freezer floor and the triangular plastic housing (it's usually held by 4 screws) at the back gives access to the evaporator and to the blower that circulates the air in the refrigerator and the freezer. There are more plastic housings that can be removed behind the white one to see what's happening around there.
If you're fine removing more parts by yourself, you can inspect the evaporator section, look for a correct frost pattern on the evaporator (if there's frost just on a part of it, the system is likely low on refrigerant).
Unlike the part you removed, if you remove the freezer floor, be careful as there are electrical wires around there and there are also more critical parts that you don't want to break. I'd suggest disconnecting the fridge to do it.
