there is a cheap special tool for removing the door card to put the mirror on. Be careful as the door card is easily damaged and the fitment to the door will not look right anymore. Use the tool and make sure it is under the head of the retainer and slowly pry each one out a little at a time! Sorry if you already know this...if not learn from the mistakes I made back in the 1970's. The old school one looks like a forked pry bar so you can secure the fork under both sides of the retainer. The scissor action tool gives you a more even pulling action and works quite well.
