If you use the right medical knowledge to help a passerby, and the passerby receives effective treatment, you will be praised in this case. But if you use the wrong way to save a passerby, causing the passerby to die or his condition to worsen, you will be legally responsible for this situation. At the very least, you should have to pay some medical expenses. If you don't know how to do it, you can call the police on 120, which is what you should do.