How to Cast an actor from another actor

If I use direct reference method, I can access an int number but its giving error and if I setup a simple function that ascends 100 cm height, I cannot do it.

This is my first actor There is only a cube inside there is nothing more

And this is my second cube. I direct referenced FirstActor. and only wanted to set new location like my question and your answer.

When I hit play I cannot see the function is worked and I get this error

The solution is very important to me. I would be very happy if you solve my problem. Because of this, I cannot advance in my own project and I feel something is very easy and I am missing that piece