In the upper-right corner of any page, click your profile photo, then click Settings.
In the "Access" section of the sidebar, click Emails.
Under "Backup email address," select the address you want to set as your backup email address using the drop-down menu.
Setting a backup email address
Use a backup email address as an additional destination for security-relevant account notifications and to securely reset your password if you can no longer access your primary email address.