Arpan you need to upload the OBC certificate in the prescribed format given on the JEE Advanced portal. The original certificate is not accepted in the JEE Advanced exam. In case if you don't have the OBC certificate in the prescribed format then you can right now upload the original certificate just to ensure you belong to OBC category and then make an OBC certificate in the prescribed format before the admission in any of the IITs as during the admission all your original certificates will be again verified properly.

Feel free to ask if you have any more queries. All the best!!