The storage box has two spring clips on the back, facing backwards. If you enlarge the second image posted by dodds turbo you can just make out a raised lip on the end of tool 3370 pushed up behind the bezel of the storage tray. The reason for removing the gear lever trim is to enable you to push the tool handle down to prise the unit out backwards.
I used a 6-inch wrecking tool, suitably padded, to get mine out. Like so many other panels on the Leon, it can take some force to remove it. Work on one side and then the other to gradually prise it out.