This app was mentioned in 2 comments, with an average of 2.00 upvotes
In your room, disconnect the xfinity modem/router combo. Connect the coaxial cable to the new modem (SB6141) and then power it up. Call comcast and tell them you want to activate a new modem you just purchased. When they do it for you, they will deactivate the old modem and activate yours. Put an Ethernet cable from the modem to the router into the WAN/Internet port. Now, you can access that router two ways to setup the wifi.
Use a computer and connect to it with an ethernet (preferred), but if not use wifi. Go to www.routerlogin.net and login with username: admin Password: password.
Go in there and set it up (recommend using WPA Personal 2 with AES) and set your wifi SSID number and PW
If you don't have a computer, use your phone (I am using android) and install the netgear genie app and connect to your router with that (your ssid should netgear24 and netgear50). Use the same password to login and change your settings.
If that doesn't work I can help you later in the day and if you're relatively close.
Let me know
It looks way better than the Netgear app.