stick a large flat edged screw driver in the gap and then twist and prize it off
Only joking - lovely mirror glass finish you've got there
Just pulls out see this link on how to: http://www.pelicanparts.com/techarticles/BMW_Z4M/05-BODY-Front_Side_Marker_Light_Replacement/05-BODY-Front_Side_Marker_Light_Replacement.htm
I would remove the indicator first before pulling out the circular panel. Hold the indicator firmly and twist anticlockwise a quarter turn and withdraw. Remove the connector from the bulb holder...don't lose the wire inside the wing !
You can now put your fingers in the hole and pull the panel out more easily.
Turn the side repeater housing anti clockwise and it will come loose. Remove that and then simply pull the circular part out using the hole left from where the side repeater should sit.