It is easy, just connect a scalar parameter node to the panner node in your material.
And do the following:-
1) Create a Material instance (not necessary but helpful)
2) Apply it to your Ball
3) In Blueprint, you can access the material through the " Get Material " node.
4) Change speed of panner through Accessing the scaler parameter by using " Set Scaler Parameter Value"
( See this :-https://docs.unrealengine.com/enUS/BlueprintAPI/Rendering/Material/SetScalarParameterValue/index.html)