Need to reset password of Admin Gateway tool.

Local login to http://10.0.0.1  on Xfinity gear?  If it was changed, factory default is the only recovery, then it's admin/password.  

Some hardware has a toothpick hole to reset (push button until lights blink).  Some just have a WPS button.  Mash that in for 20-30 seconds until the lights blink.  https://www.xfinity.com/support/articles/troubleshooting-your-cable-modem

Might be able to do it with the phone app too.  Does wipe out all settings though, including WiFi SSID's, WiFi passwords you set.  Might have to 'forget' the WiFi network, then reconnect some devices.  I don't know if theirs does a hardware encryption keygen when you default them, but if your devices won't connect, that's probably it.

Hello and welcome to Comcast. Thank you so much for reaching out to us about getting your modem admin log in reset. You are in the right place and I am happy to assist you today. In order to get the login to the modem back to default, you will need to do a Factory Reset.

Locate the Reset button on the back of the gateway and use a non-metallic pointed object (such as a toothpick) to hold in the Reset button for 30 seconds until all the LED lights power off.

If your gateway does not have a Reset button, locate the WPS button and hold it for 30 seconds. 

Please visit https://www.xfinity.com/support/articles/troubleshooting-your-cable-modem#:~:text=Locate%20the%20Reset%20button%20on,hold%20it%20for%2030%20seconds to learn more about our Factory Reset. 

reset the modem to factory default. usually there is a button to press and hold for so mayn seconds and then it gets reset like it was from the factory. you would need to look in the user manual for how to do this. xfinity should have guides or similar on how this is done..