You can correct the code during the correction window when it opens from January 15th to January 31st, 2020.  NTA will open its correction window online from 15th January to 31st January and during this period, you can login to the official website and make the necessary changes. But do remember that this is a one time correction facility and so you need to make a note of all those corrections that you want to do in your application form and then make the necessary changes and submit. Once you click on the "Final Submit" button" you cannot utilise the correction window again.