Check it in your Cpt marksheet
or the letter of registration of Cpt received by you from ICAI
Send a mail to student help mail id of your respective Regional office with Name, DOB, Address, and Father's name.
you can check your email
ICAI sends registration no on mail n phone no
so you can get it from there
if you don't have these then better call ICAI helpline number 1800-200-2501