What do you mean, exactly?
Is it building up excessive frost, and you have to defrost it frequently?
Frost is normal to an extent, both inside the freezer and on the fins in the fridge; the coolant is freezing the moisture that's in the air, or coming from the foods you put inside.
First I would check the gasket around the doors; if this is stiff instead of supple, it may not be sealing correctly, letting moist air inside.
You can replace this (expensive) or possibly augment with foam window weatherstripping.
Next, make or buy a tiny 12 v fan to blow on the cooling fins inside the fridge; this will help with the air circulation and keep your food at a more even temperature as well. There are pictures and discussion on this thread
Look for the tiny clip on a wire that is attached to your cooling fins inside the fridge box; that the thermistor. Try moving it lower on the fin or to the next fin to the right, and see if that changes the temperature and helps with frosting.
Putting some 12 v fans in the fridge's chimney stack will help the fridge efficiency by moving air more quickly past the hot coils; they can either blow up at the bottom or exhaust from the fridge vent on the roof. We installed 3 12v computer fans just under the vent cap.
Make sure you spend the minimum amount of time with the doors open; no standing and saying "Hmmm, what do I want to eat???". This makes a big difference in these tiny fridges.
Try to put only cold, dry food in your refrigerator. Let hot foods cool to room temperature first and get cold food back in the fridge quickly.