What in particular do you need assistance with? You should be able to create a socket on the skeletal mesh that is attached to the hand. After that, you can create a collision box, sphere, or any collision shape that you want and attach it to the socket.
As far as calculation, it should work the same way. You can use OnComponentBeginOverlap from the collision volume that is attached to the hand and use the OtherActor or OtherComp pins to Cast To your enemy blueprint or it’s collision component, depending on which you choose. From the result of that cast, you should be able to deal the damage there by subtracting from the health or calling a function you have set up to do this.
Things will be more complicated if you’re doing damage overtime, multiple hits, or being able to hit while moving but a few booleans and/or timers should be able to sort those out.