Assuming this is not a remote that controls by infrared signals and just works without the need to be linked (in fact cannot be linked)...
Remotes that control via WiFi are linked to the Roku they are to control. When pairing, they can get confused if they detect multiple Rokus with which they can be paired. You may need to pull the power from the other Rokus while pairing the remote to the desired Roku. Once paired you can plug them all back in.
Roku Community Streaming Expert
I am not a Roku employee, only a user like you. Please, no support questions via private message -- post them publicly to the Community where others may benefit as well.
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Ultra 4850 | Ultra 4800 | Streaming Stick 4K+ 3821 | TCL Roku TV 43S245/C107X