Hi Riezez,
Yaklakootmaa is spot-on with their answer. (Using ‘random’ function).
But here’s a different (admittedly more complicated) way to do the same thing. Takeaway here is that arrays are zero-based (the first item is at position 0). So if you’re seeing ‘off by one’ problems that could be the cause.
If you enable ‘Instance Editable’ on the array variable, you’ll be able to set the actors per-BP once the BP is placed in the level.
Hope that helps!