If you want the 'Soldier' to follow the 'Routemarker' created in the same event, that's easy: just use Routemarker.X, Routermarker.Y and it will refer to the one just created. When you create an object, for the rest of the event, all actions and expressions refer to the created instance.
If later you want it to set its angle to the instance with the UID stored in its private variable, you can do something like:
+ For each Soldier
+ Routemarker Unique ID = Soldier('CurrentRouteMarker')
: Soldier: set angle to Routemarker.X, Routemarker.Y
This will check each soldier individually (instead of trying to do them all at once), find the correct routemarker, and use that to set the angle.