When you create widgets, remember to create a reference variable - this will allow you to gain access to that widget easily (now but also later on):
Above, here called Widget Reference - you can create it by right clicking the Return Value pin on the Create Widget node and then, ideally, give it a meaningful name.
When it comes to using a setup you described above, the most convenient way to pass data from the widget to the actor would be through a dispatcher, as seen in the image above. A slider already has one so there’s no need to add a custom one:
This way, whenever the slider’s value changes, this event in the actor will execute. You will want to connect the white execution wire of that event to the Set Relative Location node.