How to block a device from home network wifi

https://www.xfinity.com/support/articles/personalize-customize-hnetwork-xfi#pausingdevices 

Usuing the Xfinity app you can click on name of device that you would like gone and click on it, then click the device that you do not want on your network. And if it’s not there is a device that means they haven’t connected, so if they don’t have a password they can’t get it in :)

@user_31b383 

Was the link that I posted to that article of any use ?

Just change your password ?