I found this and will try it.
If it is wrong, please let me know.

Center Stop Lamp.

Sedan/Saloon. [Query] The high-level brake light (the one that sits in the rear window) is dead in my 1992 940. I can't seem to figure out how to access the bulbs. The manual has an unhelpful picture of a screwdriver underneath the cover with the description: depress the catch with a screwdriver. I can't seem to find this catch. [Response: Bob] There should be a hole in the bottom side of the cover. The catch is tricky to find. Keep probing and push up while wiggling the cover.

Wagon/Estate. [Response: Jay Simkin] To remove the brake light housing cover:

put the tips of your index fingers at the "sharp" corners of the housing, which are closest the the window
put the tips of your thumbs at the rounded corners of the housing, closest to the sharp corners.
using the tips of your index fingers, pull each side of the housing outwards about 1/16" (i.e., towards the gas struts that hold up the hatch)
pull the housing downwards (i.e., straight towards the ground). You should feel it release. It will come free. Set it aside.
To remove the brake light bulb holder:

You will see two black plastic tabs sticking downwards (towards the ground) from the brake light assembly
Using a thumb and index finger grip each tab and press inwards about 1/16" (i.e., towards each other) while pulling downwards gently
You will see and feel the bulb housing release from the mounting.
To remove the brake light bulb:

Grip the bulb gently and press downwards gently (as if you were trying to press the bulb into its fitting). You should feel some "springiness".
Turn the bulb. If it does not move, turn it in the other direction. It should release and "pop" free.
Replace the bulb, with an exact replacement.
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