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I assume you mean the settings for enabling the account in an email client like Outlook or Thunderbird or some other? If so the settings are found here----------
It depends on how you are accessing the account. Are you on a desktop or laptop computer using an email client like Outlook or Thunderbird? Or are you on a smartphone or a tablet or what?
Assuming you are using Mac Mail, in the left Mailbox panel, right-click on the Comcast account. In the menu that pops up, click on Edit. In the dialogue that comes up, click on Advanced. There you will see the field to change the incoming port number. Leave SSL checked, and for Authentication it should be Password.
OK you're one-up on me. My Mac is too old to update to Sierra. I'm still on El Capitan. Try deleting the account from Mail, then re-create it from scratch.