Hello,

You may be able to add another subject during the application correction window, but this depends on the specific rules and guidelines of the exam conducting body. Here's what you can typically expect:

1. Review the official notification for correction window details.
2. Check if the additional subject option is available.
3. If allowed, log in to the correction portal and select the new subject.
4. Ensure the payment for the new subject, if required, is completed.
5. Contact the exam authority if there is no clear option.

Check the official exam website for the most accurate and updated information.

For accurate and detailed information, please ask your query with relevant details like examination name etc.

Hope it helps !