Not real familiar with the 190E series, but I don't believe there is a trunk release or gas filler release lever for those models...in fact, NONE of mine have any such device...probably an MB thing...
You may have an actuator that "locks" the gas filler door in place when the ignition is on or the car is locked though...
2009 ML350 (84K) - Family vehicle
2001 CLK430 Cabriolet (71K) - Wife's car
2005 BMW 645CI (124K) - My daily driver
2012 Mustang V6 (60K) - Daughter's car