bmw 118d left alone 1 year.

i got a bmw 118d,year late 2006,122hbp.i left home,so the car now is not
driven for approximathely 1 year.what is the less wrong: if i dont start the
engine at all, or i start the engine for how long?periodically in each 2
weeks? each month?if engine started needs to run fiew miles or its inough
to keep running 20 minutes 30 minutes to worm up?(i need to ask one of
my relatives who is at home to start the engine if its needed.)