Right now, I think you'd have to edit the app. Peer David wrote it (I can't find him on the forum, but you could open a GitHub issue on https://github.com/espruino/BangleApps and mention user @peerdavid?
Espruino is a JavaScript interpreter for low-power Microcontrollers. This site is both a support community for Espruino and a place to share what you are working on.
Right now, I think you'd have to edit the app. Peer David wrote it (I can't find him on the forum, but you could open a GitHub issue on https://github.com/espruino/BangleApps and mention user
@peerdavid
?Otherwise you could tweak it yourself. The temperature code is at https://github.com/espruino/BangleApps/blob/master/apps/lcars/lcars.app.js#L161 and there's actually a 'locale' module https://www.espruino.com/Bangle.js+Locale which would display temperature in the right units for where you live