If you have been selected to be a deputy, then you need to sign-up for a deputy vaultbox account in order to process unlock requests.
You will have received a mail from vaultbox informing you of the request. Click the link that says "Sign Up", and you will see the following screen:
Enter your details then click 'Next'. You will also need to set up Multi-Factor Authentication.
Note that as a deputy, you do not have your own vaultbox. If you would like to upgrade your account, go to X and click Y.