Set value to a specific controller

I would like to make server set value to a specific client’s controller, but i have no idea how to do it in c++.

This is what i done but the result is not what i want.
I call a function, firstfunction(…) with property (BlueprintCallable) from blueprint.

and then i call secondfunction(…) with property(Server,Reliable,WithValidation) from firstfunction(…)

i call thirdfunction(…) with property(NetMultiCast,Reliable) from secondfunction(…)

and finally return a value which should already set in thirdfunction(…)

but the first return value is 0. but the second return do have something i want

Can some 1 help me in this?