I want you to take a look at that last image of your character blueprint, and consider how you plan to determine whether the actor is an enemy or not, and what is missing from that picture. If you still can’t get it, take a look at the previous image of the blueprint.
To communicate between the Character and the HUD, create a boolean variable on the HUD to control whether you are looking at an enemy. On your character, after you have determined whether you are looking at an enemy or not, get the Player Controller, and get the HUD from that player controller. Cast the HUD to your HUD blueprint, and set the aforementioned boolean variable to the correct value. In your hud, simply use a branch or a select node to determine which image to show.