Open up an Administrative level Command Prompt and run tasklist  or netstat -ano | findstr :portNumber to see all of the running processes:

C:\Users\Hussain>tasklist

C:\Users\Hussain>netstat -ano | findstr :portNumber ( in this case port 3000)

C:\Users\Hussain>Taskkill /PID /F

Below is the screenshot of the above steps performed.