The Fire Stick remote is Bluetooth, once its paired to actual Fire Stick, then you go into the settings on the fIre stick and program it for a tv. You'll find Roku tv's listed among the tv brands. You cannot pair the Fire Stick remote directly to any Roku device, Roku devices do not use Bluetooth. Instead use a completely different RF called Wifi-Direct.
So do you have an actual Fire Stick connected to hdmi input on the Roku Tv?
Edmund
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