Mortise locks include several working parts assembled together with springs that allow retraction of the latch when the lock handle is turned. Reversing the latch is common, requiring the removal of the lock body screws. This is a simple task, but care must be taken to place the parts and screws in a secure container when disassembling them.
Remove the screws from the side of the lock body.
Remove the lock body side.
Remove the latch by lifting the latch assembly out of the lock body.
Turn the latch over with the bevel facing the opposite direction of the original assembly.
Compress the spring and washer and press the latch in place, making sure the latch aligns in the lock body's guide slots.
Install the lock body side, apply thread lock to the screws and install them in the lock body side.
Rubber gloves will prevent grease from getting on your hands when touching the lock parts.
The screws are quite small, so use a container to store them during disassembly.