Making the SSID visible is something controlled within the router configuration page. I can't say exactly where to find it, as every brand labels things differently. But it should be found under wireless or radio.
The next question is if you have only a 5 GHz radio enabled on your router. Assuming the router is dual band, it has radios on both 2.4 and 5 GHz. If for some reason your 2.4 GHz radio is disabled, your Roku will never see it, as the Express+ (all versions) only have a 2.4 GHz radio.
If the 2.4 GHz radio is enabled, then I'd suggest trying a different channel. Most routers by default are set to Auto for the channel they use. While the Roku supports all 2.4 GHz channels, it's possible you might have a better connection using a different channel. Again, I can't say where that setting is in your router, but it will again be somewhere under wireless or radio.
Dan
Roku Stick (3600), Ultra (4640), Ultra (4670), Premiere (3920), Insignia 720p Roku TV, Sharp 4K Roku TV, Nvidia Shield, Windows 10 Pro x64 running Serviio and Plex on a wired Gigabit network.
