Hi

Get in touch with the authorities. You can't download the admit card unless you enter registration no, date of birth and mobile no.

" Candidates are advised to check all the details mentioned in the JEE Advanced admit card 2021 carefully and contact the Chairman, JEE Advanced 2021 of the respective zonal coordinating IIT in case of any discrepancy. Candidates can also contact the Chairman of zonal IIT in case of any problem in downloading the JEE Advanced admit card 2021."

https://jeeadv.ac.in/contact.php

Hope this helps!