You can determine your Roku model from Settings/System/About on the Roku device.
If you have the Roku Premiere 3920, then it is a 2.4ghz-only device.
Try connecting it to a mobile hotspot (if available to you). Make sure you have your hotspot set to use the 2.4ghz band or "maximize compatibility" enabled in your hotspot settings.
Not seeing any networks is usually a hardware failure, but not always. If you currently are using your TV USB to power the device, try using a power adapter at the wall to see if maybe just a power supply issue. (any 5volt, 1amp USB cell phone charging adapter should work).
If the device is still not seeing any networks and does not see your hotspot, then last resort is to try a Factory Reset. (press and hold reset button for 30+ seconds. (make sure you have a working physical Roku remote before performing a factory reset).
If you do not have a mobile hotspot available to you, then definitely verify that the 2.4ghz band is enabled on your router. (the 3920 cannot see or use the 5ghz band).
