Change object's (parameter) variable in a World Method.

I have 40 squares (tile) each with a "HidingObject" object variable I added in via the Properties Tab.



What I am trying to do via a World Method is assign other objects to it.

HOWEVER



What I am trying to do is set

Tile.HiddenObject set value to Object
Bolded items are parameters.

However, it will not let me specify a parameter, to access its variable.

The only solution I see is to do an IF statement for every square I have. (40 if statements)



So in conclusion

I am trying to change a variable of a object, specified via a parameter of a world method.

Help would be appreciated