Step 1: Create a second member account
In the backoffice, create a second member account with the email you wish to associate with it.
Step 2: Fill in the form
Fill in the form with the new email and save
Once the second account has been created, all you need to do is merge the two members, with the help of this article
Warning: If the email indicates "disabled", contact your Account Manager to resolve the problem. Do not merge.