When you remove the black outer cover, you'll see a white inner cover, with 2 sets of clips, one at the top and one at the bottom.
Pinch the clips with a thumb and forefinger whilst pulling and the white plastic bulb holder will pull out.
There are 2 reverse lights on the A2 and hopefully, they will have blown, as otherwise, it points to the reverse switch being broken, which is much harder to change than a pair of bulbs.
Cheers,
Mike