To start the process, access the portal: Electronic Office – CNMC Alias Registry Management

Select access with cl@ve or with an electronic certificate, as applicable:

• Spanish companies must use a valid Spanish digital certificate.
  
• Foreign companies in eIDAS countries may use their compatible local digital certificates.
• Foreign companies without an eIDAS certificate will need to obtain a Spanish tax identification number (NIF) beginning with the letter N, for foreign companies, and subsequently obtain a Spanish digital certificate in order to complete the registration.

Once authenticated, the system will automatically identify you and you will be able to start a new registration.