If the software had been uninstalled in the normal manner from those devices the licenses would have been freed up but Customer Service can do that for you, they are free to phone or you can use online chat, but for this it's best to speak with them, link is below.
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Please confirm whether "roku" is the Device name or a new Device. You may look at the icon next to it to identify if it is a mobile device or a PC. Perhaps a Screenshot of the My Account page will help.
With regards to freeing up License you need to De-activate these three devices so that their Licenses can be used for a new machine. If you don't see the Deactivate option in My Account page please call on Support as instructed above.