I have had to sort mine twice in the 3 months of ownership on my 97 E92. If its just sitting proud of bumper then you can adjust the springs to make them fit flush again, I've done it today & it took 5 mins now that I know what I'm doing.
1) Carefully pull out flap slightly to reveal washer jet ( flap is attached to washer jet by 2 springs which are connected to a clip that fits onto washer jet)
2) Using some form of hook ( I use a thin metal skewer bent 90 degrees at the end) pull out the washer jet, it will retract if you let go so be careful & it is quite stiff to pull out but you won't break it!
3) Remove the flap by uncliping from the washer jet.
4) Depending how bad, either just compress the springs tightly or remove springs completely from the clip then compress using some pliers.
5) Refit & let the jet retract, it should now sit flush or it has done for me. It will go again but is a temporary fix, I will remove the fuse I think to eliminate the problem but shouldn't have to, it's a really bad design by BMW!
Hope this helps.