I know that this topic has been listed before, but it is such a normal failure and such a easy fix, so i repeat it.
It's part 11/12
1 Remove the plastic cover to locate the screw (torx) 20
2 Pull back the seatcover to locate the screw for the lever (torx) 25
3 Pull out the broken lever and replace with a new. (BMW has modified the lever so they are stronger than the old ones.)