The 190 rear bumper is attached to the car with 6 bolts in total. There are 2 bolts (17mm wrench if I remember correctly) under each taillight in the deeper well of the trunk just besides the chassis beams. These can be loosened to re- adjust the rear-side of the bumper.
At each side is one bolt (10mm wrench) that will take care of the alignment of the side of the bumper. These adjustment bolts will make it possible to rotate the sides of the bumper in regard of the rear.
The side bolts can be reached through a possible "door" in the quarter panel upholstery at the inner side of the trunk or after removing this upholstery (if the "door" is not present...).
If the side of the bumper was hit by something, it is possible that the plastic clamp at the side of the bumper is broken. These can be exchanged (after removing the bumper).
You can re-adjust the side of your bumper as well. There is a plastic guidance at the side of the bumper that has to be loosened after which you can push it up and fasten it again to match the bumper height with the bottom of the fender.
It is the easiest way to re-adjust the side of the bumper after you removed the lower part of the dirt panel (under the fender/behind the bumper).
If you want me to, I van send you some pics of the mentioned guidance and the dirt panels...
with a minor 600+k