All the routes you create (see how to create a route with Suunto app for iOS here and how to generate a route from a workout here), import (find out here how to import routes from .gpx files to your iOS device), or transfer via a partner service to your Suunto app account are conveniently stored in your account’s route library. From there you can edit them, share them, choose which one(s) to transfer to your watch, and delete them.
Tap on a route to see its details and edit it. You can edit the suitable sport mode(s) for the route (you can select more than one sport mode for each route if you want), activate turn-by-turn guidance, and toggle or un-toggle the “use in watch” option; by tapping on the three dots on the top right, you will be able to edit the route itself, rename it, or delete it altogether.
All the changes you make will be visible in your watch after the next sync.