To rotate an object in your Scene
Make sure you are in the Scene Creator and not the Model Creator
Select the circle with an arrow on the editor toolbar. This will put your object into rotate mode
Select the item you want to rotate by clicking on it, or selecting it from the object tree
You will see three arrows which represent the three axis of rotation. This widget will be at the pivot point of the object. If you can't see the widgets, click and drag the background to rotate the camera until you can see it.
When you hover over one of the coloured arrows it will turn yellow. This means it is active and you will be moving the object on the arrows axis
Click and drag to rotate the object back and forth in the chosen direction.
You can also enter specific values in degrees in the Transform section on the bottom right of the Properties menu