If user forgot their password. There is on option called to be as forget password. Input your email id on that box and click on submit button.then you get your new password regarding to your email-id. password is either come on your cell or some referenced id which you give on the time of registration .
This is good advice for a forgotten password. However, the OP wanted to change an existing password with both the service provider (Verizon) and with his e-mail application (Thunderbird).