The covers on the wing mirrors can be detached by levering the mirror glass over to an angle so that you can see inside the mirror housing to the double clips. There are 4 main ones that can be squeezed with a pair of long nose pliers releasing the cover from the housing. They aren't designed to come off once fitted but with (admittedly a lot of) perseverance they will release, you may snap one or two of the double clip sides but there should still be enough remaining to clip it back on securely
Dave J
July 2008