Here’s the most basic implementation:
The widget with the slider calls its own Event Dispatcher and sends Slider Value to any object that will register with this event:
In the Level Blueprint, I manually dragged & dropped a reference to the Floor from World Outliner:
Begin Play adds the widget to the viewport and binds the widget dispatcher call to an event in the Level Blueprint:
The rest is getting the scale from the Floor reference and setting it back to what the Map Range node spits out. It scales only one way here because the pivot in the blank template I used it set up like that:
If something does not add up, do tell.
tip: you can right click pins and split them (break them into components) - like the vector of Get Actor Scale 3D node above.