Button to open door broke; need to open to uninstall & install new one

Hello - the microwave door on our GE microwave has broken. When the button is depressed to open the door nothing happens. A new microwave has already been purchased along with a new trim piece. We need to get the old microwave open in order to unscrew the trim plate (the microwave is in place in the cabinetry). Whats the best way to do this? There is no intention to keep the old microwave so damage to the device isn't of concern. In fact, it's already been set up to take the old one to the store where the new one was purchased for recycling.