You can enter this ID into the mobile apps, or set it on another device.
set ID #####
Where ##### is the ID of the account you want to track.
You need to speak the ID as individual numbers. If the ID is 12345 you should say "one two three four five." This may take a couple tries, but don't be afraid of messing up it will ask for confirmation first and there is also a restore command if you make a mistake.