Hi, I did it. You should install and run the emulator manually from MS website. I suppose that you have done that already.
UE4.23 don’t support direct run on the emulator from the editor. When you have started the emulator, click to Device Portal icon (with a little globe). The DevPortal will be opened.
Compile a project with emulator support (select it in Project settings/HoloLens)
Then go to Views/Apps/Deploy Apps, click Browse, find your package and click Install. When a package will be installed, find it in Installed Apps, select and click Start.