Create a new Actor Blueprint and add a Get Actor Of Class node in the Event Graph connected to the Event Tick node. Select TouchDesignerConnectionActor as the Actor Class.
Start dragging from the Return Value into the empty space around it and select Received Values from the list of possible nodes that pops up. Now you have the list containing all values (indexed by the channel names in TD) sent from TouchDesigner.
With a Find node you can get the value you want out of this list. You can use that value (of type float = number) to control other properties.