Comcast engineers, in their great and awesome wisdom (sic), seem to have removed the ability to do this from ALL of their gateways within the past couple months, whether you have (or had) Pods or not.
There may be some lucky people who still have not been "upgraded" to this awesome (sic) new service but I would assume by now that those numbers are very few. If you dig through the painfully designed forums here you will see numerous complaints about this silent change and you will hear the sound of crickets in response because Comcast 1) doesn't care about you, 2) they don't really monitor these forums, at least with anyone with any real technical knowledge and, 3) the few who do preuse here will ACTIVELY avoid anything touchy like this topic that they know they will get beat-up on as they have no input back to the non-smart (can't say a "naughty" word you know) engineers back in Philly.
Sorry to not be of much help, but this issue really burns me up. Anyway, your best bet is to just bite the bullet and get your own router and modem and then you again have the most basic of wi-fi controls back in your hands. Maybe the new white Wi-Fi6 gateway they announced will be better, but I'm not holding my breath. It's a shame when a company won't let you throw money at them every month (rental fees) for doing something so dumb.