As of v1.0.0: the only way for Windows users to switch between DirectX 12 and Vulkan is to head over to config.toml under the Configuration file, and change this under [Video].
GraphicsAPI = "Auto"
to
GraphicsAPI = "Vulkan"
For those who prefer Vulkan over DirectX 12 on Windows OS, it would be ideal to add the ability to change that within the Graphics Settings in-game.