Go into "Sessions > Routes" and use the different options on the left to find the route you want to ride. You also have the option of searching on the map if you want to focus on a particular area.
When you hover over the route profile, the "Schedule" option will appear. Clicking on it will make it available for you to ride in the Simulator.
Use "Set up" to customize the session, add opponents or bots, splits, or cadence or zone objectives, even the date to ride it. Follow the steps to set it up to your liking in the simulator.
As you can see, it's very easy. In a couple of minutes, you can be on the bike riding anywhere in the world.