I suppose you are talking about the CUET application form. If you have selected only English in Language From Section IA and didn't fill any domain-specific subject, you can make the changes when the correction window opens. To know the dates for same follow the official website. https://cuet.samarth.ac.in/

However, if you do not make the changes in the correction period your application will surely be rejected and you will receive a message vis email for the same.