Steps are supported in OSM, but I don't know if your ones in particular are tagged. Either way, Trail Router doesn't consider them by default. If there is a lot of elevation gain/loss when using the stairs, you can adjust the Hill Preference slider (in the settings screen) to indicate whether you prefer hills or would rather avoid them. You can read more about that here: https://trailrouter.com/blog/greenery-and-hills-sliders/