You can split the lights carefully with a pair of pliers and pry it open with a screwdriver.
Sean's preferred way: You can also put the flowlight on a hard durable surface with the seam facing up and hammer it along the seam on both sides. You could use an empty beer bottle or a metal pipe or similar round hard and heavy object. A hammer works but might mar the shell. Start with soft strikes, and increase force if needed. You should be able to split the seam without deforming the shell.
You can reseal the shell with thickened crazy glue, thickened cyanoacrylate or polycarbonate glues, but it has to be done really cleanly. You might also use small strips of clear tape to make rings around the shell to hold it together. The shell will never be as well-sealed as the original, because the original is ultrasonically welded.
Hope that helps and please don’t hesitate to contact us if you think of any questions! =-)