Hello Brad. You can use the Home Network Manager to modify your settings at any time.
Once logged in, Click Wifi on the left side. If your current Network is using both 2.4 and 5G, uncheck the 5G, then click the + sign near the top to add a new network. On this new tab 5G is set by default and you can make the SSID and password changes among other settings. If you have already tried to add a guest network, you may need to select the guest network and click remove network in order to continue with the above instructions.