5G and 2.5G

Open up your Xfinity app.  If you don’t have the app download it from Google Play or the Apple App Store. When you open up the app go to the Wi-Fi tab and click on the box that says Wi-Fi details.  You will see what networks you do have. I have 2.5 and 5. The kindle eReaders and Ring doorbells require 2.5.  Although if you have Xfinity Wi-Fi extenders you may have only one network. You could call for technical support to find how to change that or someone here can possibly help you. 

Like @Lkpolo said.  Option might exist or not depending on what you have for Xfinity equipment.  Some radio chipsets work with band steering/combined signals, some don't.  The documentation is poor, but from this link and the "notes" section:  https://www.xfinity.com/support/articles/view-change-wifi-password 

• If you have xFi Pods or if WiFi Intelligence is enabled on your account, the ability to edit your WiFi name/password through the Gateway Admin/MSO tool (10.0.0.1) is disabled and you'll need to use the Xfinity app.
• If you're unsure if WiFi Intelligence in enabled, you can check in the Xfinity app by going to WiFi, choosing View WiFi equipment, selecting Advanced Settings and looking for the option “2.4 & 5 GHz.”
  • If the option is not there, then WiFi Intelligence has been enabled.
• WiFi Intelligence is automatically enabled for the xFi Advanced Gateway (XB8)

@user_e1474b, Thank you for reaching out through Xfinity Forums with your question regarding 2.4 and 5 GHz. You need to first determine how your advanced Wi-Fi settings are managed. Here is a link that will help walk you through that process. Let us know if you need further assistance. https://www.xfinity.com/support/articles/change-wifi-mode-admin-tool-xfinity-xfi