How do I set an XB7 router to 2.4 Ghz?

I have a new SimpliSafe system that won't work with the 5 GHz signal that my XB7 router provides.   I have tried to tell the XB7 to use 2.4 gHz, but I can't find a way.  The internet says to use Advanced Settings, but also says that XB7 does not allow access to Advanced Settings.   My app does not show advanced settings, and the 10.0.0.1 link seems dead.  

Various posts have linked to an xfinity article on the subject.  But when I click on the link, all I get is a generic menu, not the intended article.