First, peel any stickers off. Feel around for any dimples that can hide screws.
Look for seams, especially around where the cables go in. Then use plastic putty knives, guitar picks and so on to pry open at the seams.
If it's newer, It could be fully welded closed, in which case you'd need more destructive techniques. An oscillating tool with something like a tile cutting bit could get through the plastic with minimal damage to the innards, but would remove quite a kerf you'd have to replace when you put it all back together.