while running the npm script (npm start) you may encounter the command, this basically occurs when we have previously run the file in same port, to avoid this what we have to do is----

go to the server.js file then
update this
Server.HTTP_PORT = WXYZ;
Server.HTTPS_PORT = ABCD;
i.e. change WXYZ to something else and ABCD to something else

then again run npm start
then it will successfully get started in the updated port address.