If you're using the Dialogue Manager prefab from Plugins / Pixel Crushers / Dialogue System / Prefabs, its Instantiate Prefabs component instantiates a copy of Standard UI Prefabs / Templates / Basic / Basic Standard UI Selector Elements.
To change its appearance, add a copy of this prefab to the Dialogue Manager's Canvas and customize its appearance. Then you can save it as a new prefab and assign that prefab to the Instantiate Prefabs component, or remove the item from Instantiate Prefabs and leave your custom instance in the scene.
Alternatively, you can add a Basic Standard Usable UI as a child of Andre and customize it. This is a world space canvas that is specific to Andre. It will only appear when the Proximity Selector detects Andre.