You don’t set the enemies’ health from it. By calling ApplyRadialDamage you define the amount of damage that actors take inside a radius. This triggers the “TakeDamage” events for every actor that’s affected. And that’s where you can deal with the effects and subtract health, like you did in the first picture.
edit: I see you are casting there, which probably means you are doing it inside the character’s (or whoever is taking damage) OnHit-function. You should do it from the rocket instead, because it is the one that causes the damage.