Hi

As you have done a mistake in mark entry for optional subject in tnea 2020 application and also you have completed the payment. So, you can't make changes in that. There is no correction window available for the tnea 2020 application.

If you want to made changes in that, you need to apply once again using a new email ID and phone number and then again pay the fee. Also, verify your details before submitting the application form.  There is no other option, you may also try to contact the authorities and ask for solution.