I don't think one can add information to the application as submitted before through any means. So probably you won't be able to do so. Although, I would recommend you to contact the official helpdesk of the AP ECET and get it discussed then can give you highlights. But the probability is higher that you won't be able to add the EWS information now.

To know more about AP ECET visit the link below:

https://engineering.careers360.com/articles/ap-ecet

The contact details for AP ECET:

Off- 08554-234678
E-Mail : convenorapecet2021@gmail.com

For the official website visit:

https://sche.ap.gov.in/ECET/UI/ContactUs.aspx

I hope this answer helps. All the very best for your future endeavors!