If it's like the LS and RX, it's in the settings menu on the display in the speedometer. Use the controls there to navigate through and find it. If it's the older (non-Gen 10) system it'll be in the main menu on the infotainment screen under Setup.
For a 2019 you should have the owner's manual still, look in there for details. (If you don't, you can download it from LexusDrivers.com).