When the Olympus FL-LM2 flash is used with the Olympus housing, it must be in the down position to fit within the housing. In turn normally this means that an underwater mode, consuming a function button, must be set on the body to enable the flash to fire in the down position.
It is possible to modify the FL-LM2 to think that it is in the up position such that the flash will fire independent of the position of the flash head. On the main circuit card there are two solder pads in the upper left hand corner (as shown in the attached picture), where moving the black wire over to the pad with the red wire is the one change that accomplishes this modification.
There is another thread on this forum with respect to modifying the flash capacitor for the FL-LM2, where the authors detail how to disassemble the flash. In short remove the black adhesive coverings on the screws and remove the screws.