458 door mirror glass

Hi, I gave my left side door mirror a whack and now the actual Glass is loose and as I am driving along you can see it vibrating, I have tried pushing it back into the housing thinking it had just come unclipped but it does not help as I am now thinking one of the clips ?? must have broken, so does anyone know how to remove the Glass ?? I have tried to prise out with a plastic tool but failed and I do not want to break the glass??, any help appreciated, Regards DM