get/change Postprocess Volume material in Blueprint?

Hello guys.
I need a help: how to cast to post process volume (for the Blendables effect) from ThirdPersonCharacter BP, not from levele BP?
I what i have now:
i made a new actor class, add component BoxCollision and Postprocess. OnCollision Overlapped by Character I get this PostProcess → get settings → and here if i break settings (blendables) - then I have a warning: “Warning Blendables - the native property is not tagged as BlueprintReadWrite or BlueprintReadOnly, the pin will be removed in a future release.”
So, can you help me - how to change blendable material (in post process) on another actor when character overlap this collision?