Facing TV Problems? Ask a TV Technician.
Hi and welcome to the site, I’m Louie. Sorry you had to wait awhile but I’ll do my best to help.
Initially, bear with us; re-confirm and post back with the complete model number of the TV.
Still, determine if there was a cable box installed by Comcast. If there is, then the channel selection would have to be done on the cable box using the cable remote and not on/with the TV.