There are not many Roku devices that work on 5 GHz. What model Roku do you have? The specific model number, please.
Of the current models, only the Streaming Stick+ and the Ultra support 5 GHz WiFi. You have to go back several generations to find any other model Roku that supports 5 GHz.
Dan
Roku Stick (3600), Ultra (4640), Ultra (4670), Ultra (4800), 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.