Data field for Kilometers whilst watch unit is set to miles

HI,

Does anyone know how I can select (or add) a data field showing the distance run in KM, even though my watch is set to miles?

On my old Garmin Vivoactive HR, I somehow managed to do this but I can't remember how I did it, and I can't seem to find a way to do it on the Fenix 5X plus.

thanks