I have faced this problem recently, you can try the following 2 methods :-
Method 1:-
- make sure you are exiting out of the previous server or stopping the previous server by pressing CTRL+C.
- Now restart the server by 'node index.js' or 'nodemon index.js'
Method 2:-
1.If above method is not working you can Try closing the terminal and again opening it
2.Now start the server ,Most prbably your issue will get resolve.