How to disconnect a device from my home network?

You need to go into the settings for the device in question and have it disconnect from your home network. xFi doesn't allow disconnection of a device while it's actively on the network. 

Thank you for your time answering my question  😉 👏

There should be ability to disconnect any device from the router by the admin.

Xifinity should consider this  😞😞

I had tried to change my xfinitywifi username and password,  reset the whole network,  reset the whole laptop by deleting all files, ... etc but they do not work. Actually,  xfinity just remembers the devices which log into xfinitywifi at the first time.  The laptop or pc do not record or save the username and password for xfinitywifi.

Here is the solution from xfinity website.
https://www.xfinity.com/support/articles/manage-wifi-devices-my-account
How to Manage and Remove Registered Xfinity WiFi Devices

To remove or rename a device registered to access Xfinity WiFi hotspots:
    Sign in to My Account or the My Account app and click or tap the Services tab/icon.
    From the Services page, under Internet, click Manage Internet.
    Scroll down to Xfinity WiFi Hotspot Connected Devices and click Manage Devices.
    Click Rename to edit your device name.
    Click Remove to remove your device from the list of registered devices. A confirmation message will appear.
    Note: If you've reached your limit of 10 registered devices, you must remove a device before you can add another.

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