You do not link one device to another. They are linked to a Roku user account. That account email address is displayed on the Settings/System/About menu. That's the email address you have to use to link the Stick to the same account as the TV. But it's not required to link them to the same account. They can be used separately, and that might be desirable if you want to have a different selection of channels on the two devices.
But if they are currently linked to separate accounts and you want them on the same one, you will have to do a factory reset on the one that isn't linked to the desired account and set it up anew.
Dan
Roku Community Streaming Expert
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