Page not refreshing after changing index.js

After I updated the index.js the ‘Hello world’ page in my browser doesn` t change.
The ‘npm start’ is still running.
What I have to do to make my changes in index.js running ?

well, save the ‘index.js’ then ‘npm i’ and then ‘npm start’
After each saving the ‘index.js’ the console on the page gets the results