Hm, i can’t find a tutorial for this. What is not working for you and how far did you come?
I need to create something like this for my game too, but i have not tried to think about it yet.
But i guess you would need to get all enemies in a specific area (like a collision sphere around your character), pack them into an array and if you press the button to lock on, you would get either the first element of that enemy array or maybe take the one in front of you (maybe line tracing and checking if the target is also in the array).
This is the general idea, but i think you would need to make this on your own. I don’t have the time to make this on the fly