Loosen the two screws and take out the brake light.
In my experience of central brake lights on other vehicles they normally have a few bulbs in them but the images I'm seeing for a 2020 Berlingo show just the one bulb, it could just be the bulb has blown.
The centre brake light can be tight so difficult to get out, when I have removed them in the past you do feel like you're going to break something.
The bulb is a wedge type / push fit, if you can't get your fingers in to pull it out you could try feeding some tape around the bulb and maybe this will help in pulling it out.
I would try to pull it out with a pair of needle nose pliers, wrap the ends with an elastic band so the pliers will grip the bulb, hold the bulb gently but firmly as near to the base as you can and wiggle it as you move it forward.
Putting the bulb back in.... either use the pliers or stick a piece of tape to the bulb to help you line it up then push on the tip to send it into the holder with a flat object of your choice.
If using tape remember the tape will have to be removed so bear this in mind when applying it!
Thanks, I tried the long nose pliers but I can't get enough purchase on it and I'm still worried about breaking it and making it even more difficult to get out.
I'll try getting the unit out again. There's a kind of small "button" on the left of the lens. It doesn't seem to move and I wonder what it does.
If I can't sort it I'll have to take it to the garage round the corner and accept it's going to cost .
I get what you're saying about the long nose pliers, if you position the legs of the pliers at the base of the bulb and rock the pliers from side to side (twisting your hand left & right) the jaws of the pliers may ease the bulb out.
Not sure about the little button on the left of the lens.
Have you tried with sticky tape around the bulb, holding the tails of the tape you could maybe pull the bulb forward out of the socket.
I don't think the central brake light is an MOT failure, but maybe that depends on the tester.
Central brake lights often have a neoprene type gasket between the light and the body and this gets a good hold, you would think the light was bonded in place with some of them.