Licence Plate Light: Unit Won't Budge

[Yaris Will]

Hello all, this is my first post here. I'm the owner of a 2005 Yaris Hatchback, in good shape generally and still with only about 89k (km) on it.

I need to change the licence plate bulb and have found a few videos showing how it should be done, and how straightforward it should be, but I'm finding it impossible to lower and remove the case that the bulb is in.

I enter a flathead screwdriver into the slot on the side and try to get the housing to come down, but it will not budge. I have tried the slots on both sides without luck. I am afraid of using too much force and snapping the tabs off or causing other damage.

What I find odd is the illustration from the owners manual (image below). It shows a second screwdriver (on the left) but I'm not sure what it's meant to be doing. None of the videos or articles I've found online mentions this sort of screwdriver. There's also no apparent slot for it. Anyone know?

Also attaching a photo of the light unit from below.
Thanks very much for any light you can shed