On the "Home" page, in the "I Want to" section, selet "Add Third Party Access"
On the "Home >> Add 3rd Party Passphrase" page:
In order for a third party to gain access to your accounts, you must provide them with your account ID number, the zip code associated with the account, and a passphrase that you will create on this page
Add a third party passphrase as the "Add 3rd Party Passphrase" page instructs
Give the passphrase to the 3rd party you wish to add.