First of all, we need to find out the process id also known as PID of the running process on a specific port. For example, a process is running on port 3000. To find its process id, execute:
lsof -t -i:4200 63562
Now you have the PID ‘63562’ of the process running on a port. Use the kill command to terminate that process by its PID.
sudo kill -9 63562
There is also a short version of killing the port.
sudo kill -9 $(sudo lsof -t -i:4200)
Hope it helps.