You may need to collect more images and train your model again. In my videos, I collected 100 images per object. You may need to collect more than I did if your object is small or difficult to discern from the background (or your camera is moving, ect).
Also, after you collect more data and train your model again and export it to ONNX again, delete the *.engine file in your model’s folder. Otherwise TensorRT will use your old model instead of the new one.
The threshold option is changed when you run the inferencing program - detectnet/detectnet.py