Since u201caddingu201d the mobile number is being mentioned, I will assume that initially the Aadhar card is not linked to any other mobile number.If no mobile number is associated or linked with your Aadhar card, in that case you will have to visit a Aadhar Kendra, or Aadhar Enrollment centre. There, you can apply for Linking mobile number, a form will be available for that purpose. You will have to produce your Aadhar card, fill the form. Your Biometric information will be verified at the centre, and the information will be updated/added. At the same time you can also update your other details if you want, like your photo. There is a small processing fee involved and you should get a receipt for your payment.However, if a mobile number is already linked to your Aadhar card, you can easily update at the online portal on the UIDAI website. Complete information on procedure is available on UIDAI - Official Website.Links:All the Aadhar Card services and information can be found at: UIDAI - Official Website. Please visit the website to get all the details.Check your mobile link status: https://resident.uidai.gov.in/ve...To update your mobile number if already another mobile number is linked to your Aadhar card ( All links are taken from UIDAI - Official Website):Instructions: https://ssup.uidai.gov.in/web/gu...Online portal: https://ssup.uidai.gov.in/web/gu...