I've changed mirror covers a few times. First one takes ages as you are scared you'll break something, but second one takes 2 mins once you know how. Pretty easy.
The instructions from Holden are useless. Hold here and here where indicated don't work too well on curved, polished surfaces. LOL
Was able to pull up the scalp at enough at bottom and slide a credit card / drivers licence (flat screwdriver and tape not required) in to help push the retaining clips away. Work it along the lip gently for a bit whilst pulling up then you'll hear ....CRACK and off it comes. You'll go looking for plastic bits all over the shop but surprisingly, he comes off in one piece.
When fitting start by slotting the top lip in and gently apply presure and it's slips in.
Refer link to previous thread for Holden instructions etc.
Genuine Holden Chrome mirror covers
Cheers
Front wheel drive cars are the work of the Devil.