Hii

You have not mentioned about the exam you are talking about. If you mention it, it will be easy for me to help you in solving your query.
In general, for any application form there is a specified time for which you can apply or correct any discripency. Once the admit cards are released it is not possible to change any detail in the application.
So i dont think its possible to make the change you want. But yes to be more sure you can mail your query to the authorities so that you can be sure if there is any possibility to make the change.

Thanks!!