Hi Resmi,

I understand that you have forgotten misplaced your registration number for the board examination that you are referring to and so to answer your question firstly check your phone and email for any confirmation email or text messages that you have received from the board which contains the registration number of your candidature. Itis highly likely that you can obtain new registration number from the above methodology and if you are not able to do so so then you are requested to kindly address this matter to the competent authorities through post or via email while  clearly stating the issue that you are facing and mentioning the relevant data associated with your candidature and request them to provide you with your registration number at the earliest.

Best wishes!