If you have the trains already placed on your route, you can make them yourself:
- Place the train down somewhere on your route
- Go to the consist menu
- Click the 'get' icon (the little grabber), or press 'G'
- Click onthe train on your route. A box appears asking you to name the consist. Click the tick once you're done
The consist should then be saved in the list for you to use later.
Hope that helps