You can download it from the Microsoft Store
Amazon is releasing its Alexa app for Windows 10 today. While the app has been available on select Windows 10 laptops recently, today marks its launch in the Microsoft Store for all Windows 10 PCs. You can download and install it on any Windows 10 PC, but only compatible devices will support Alexa wake word functionality. If you don’t have a compatible PC then you can hit the button within the app to speak to Alexa, or invoke the assistant using a keyboard shortcut.