As per the official brochure, the students have to mandatorily submit the EWS certificate/ Caste certificate (if applicable) in the portal with in 2nd October,2021. So you must check the portal where you have filled the form and there will be option for uploading the document.

For the official website you may visit:

https://jeeadv.ac.in/

To know more about JEE ADVANCED visit the link below:

https://engineering.careers360.com/articles/jee-advanced

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