Hi Simone
That is not possible since the MobileNetSSD model's weights and biases are specifically configured (through training) to be able to detect all 20 different classes. If you wish to have a model only look for a single class (person), you would have to retrain it completely.
https://blobconverter.luxonis.com/ --> Openvino and Depthai model zoo should have MBnetSSD models designed for person detection only.
Thanks,
Jaka