Your RokuTV should be capable of connecting to either the 2.4gz or 5gz bands of your network. Even if your router is broadcasting a single SSID (single network name), your RokuTV should be able to connect to the 2.4gz band at least if your 5gz band is not configured properly.
Try doing a network reset at the RokuTV. Settings..System..Advanced System Settings..Network Connection Reset..Reset Connection
This should automatically restart TV. If not, then do Settings..System..Power..System Restart
Restart your router before resetting your RokuTV Network Settings. You may have to press SCAN again a few times for your Network to appear.
If your network still does not appear, then most likely you will have to verify you have proper settings in your router....
1. both the 2.4gz and 5gz radios are enabled and broadcasting
2. Under Wireless Settings in router, 2.4gz needs to be set to a channel between 1 and 11. Do not use 12-14 even if these are options. If set to Auto, needs to be connecting to your devices at one of these channels, 1-11. Other settings should at least be least b/g/n(Mixed), 20 mhz Bandwidth.
3. Under Wireless Settings in router, 5gz needs to be set to a channel between 36-48, or 149-161. Roku devices will not operate on channels 52-140. If you cannot get the above channels, try lowering your Bandwidth setting from 80mhz to either 20mhz or 40mhz.
If you download a wifi analyzer app to your mobile phone, it can quickly help you to understand how your network is configured.
If you still have problems, post back your router model number and any information you have discovered from the steps above. It is likely just a network configuration in the router since the RokuTV is seeing neighboring wireless networks. Note any LED lights you are seeing on the router also.