Please have Comcast share how to reset change old pw in email after login pw changed.
venmartin Changed status to publish August 6, 2019
To change your password after logging in, you should check the option Manage Users and Settings on Comcast. Should you like to reset it, then visit the website xfinity.com. See where the option to enter your username is. Here itself, you will find a button to reset your password. 
You may also check this link to see more information: https://www.errorsdoc.com/email-support/how-to-change-recover-comcast-email-account-password/