How do I replace the side mirror glass in a 2004 WRX?

My aged but well-loved 2004 Subaru WRX wagon has been passed on to my youngest as the going to college car. Unfortunately, 2020: the car has sat largely idle for more than a year now. During that time, somehow both the driver and passenger side mirrors decided to crack. There’s no indication of impact and the mirror controls still work fine.

So, the question is: how do I replace the mirror glass in those housings so the reflection is a little less surreal?