Diagnosis
Soggy bottoms are almost always an overcrowding issue. You're putting in too much food at once, which blocks the hot air from circulating underneath the basket.
How to Fix It
You need to cook in smaller, single-layer batches. 1) Don't fill the basket more than halfway. 2) Shake or flip the food halfway through the cooking time. For things like fries or wings, give that basket a good shake every 5-7 minutes. This moves the pieces around so they cook evenly. 3) Pat your food dry with a paper towel before putting it in. Moisture is the enemy of crispiness.
If That Didn't Work
Try preheating the air fryer for 2-3 minutes before adding your food. Just run it empty at your desired temperature. This gets the element and the air inside hot right from the start, leading to better initial searing.
Heads Up
This is a compact model. Its power is perfect for 1-2 person portions, but it can't handle a full bag of frozen fries all at once. Respect the capacity, and you'll get much better results.