I have several Rokus and several Echo devices. I have enabled the Roku skill in Alexa, and I have been able to set up some of my Rokus to be controlled by the Echo that is in the same room with each of them. To accomplish this, after Alexa has found my Rokus, I "Edit" each Roku device and in the app I select "Linked Alexa Devices - Manage", and it takes me to a screen that lists all of my echo devices, I can select one or more of my Echo devices to control that particular Roku. The list also shows me which Echo devices have already been assigned to a Roku with the message "Already paired with a device".
The app WILL NOT let me pair a new Roku to an Echo that is "Already paired with a device" and that is my problem. I want to move one of my Echo devices into a different room and assign it to a different Roku from the one it used to be assigned to. But I can't find ANY way in the app to accomplish that. The app won't let me select an Echo device that is already assigned, even though that's the device for which I want to change the assignment. And I can also find no way to simply "remove" the old assignment from any of my Echo devices. So I'm stuck. All of my Echo devices appear to be permanently "locked" to the first Roku I assigned them to, and I can't figure out any way to switch one of these Echo devices from an old Roku to a new Roku.