You can't if the original Roku tv remotes are IR only. There is no second IR code address available. But what you can do is switch both tv's to wifi voice remote, a Roku wifi remote will only control one Roku device at a time. Both Roku tv remotes have to be replaced!!!
Amazon.com: Roku Voice Remote (Official) for Roku Players, Roku TVs and Roku Audio : Electronics
Edmund
Roku Community Streaming Expert
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