my wifi router is dual 2.4GHz and 5GHz but my Fire 7 5th Generation can only locate the 2.4GHz signal. I have manually tried

[lrfce75]

Fire 5th Generation not locating 5 ghz wireless signal

 

[webworkings]

Even if the modem router can access both does not mean both are turned on. Even seeing the lights for both doesn't mean both are turned on. I have the one turned off on mine, yet the light still stays on and blinking.

To know for certain if it has both turned on and accessible, you are going to need to get into the modem/router settings. I would also suggest that you rename one of them, as sometimes a device will see one name and only allow access to one of the WiFi. So rename at least one of them.