You have two options:
ONE: Forward the mail to Comcast: Automatic email forwarding in Yahoo Mail
TWO (and better): Fetch the mail from Yahoo to your Comcast account.
At Comcast, add an external account: Add External Email Accounts - Xfinity Connect Help
Use the Yahoo IMAP settings: IMAP server settings for Yahoo Mail
For more information login help visit our site: emailloginhelp.org