You can't. The TVs use an IR remote, not Wi-Fi Direct, so any Roku IR code in the room will be seen by both. The only thing you can do is to block the IR receiver window on one TV (I can't tell you exactly where that is, but somewhere near the bottom left) and use an app on your phone or a tablet to control it. Then the IR will control one TV and the app controls the other.
Dan Roku Stick (3600), Ultra (4640), Premiere (3920), Insignia 720p Roku TV, Sharp 4K Roku TV, Nvidia Shield, Windows 10 Pro x64 running Serviio and Plex on a wired Gigabit network.