Thank you, I followed your advice and got it to work!
GeometryCollectionComponent.h
/** Sets a new Rest Collection. */
UFUNCTION(BlueprintCallable, Category = "ChaosPhysics")
void UpdateRestCollection(const UGeometryCollection* RestCollectionIn);
GeometryCollectionComponent.cpp
void UGeometryCollectionComponent::UpdateRestCollection(const UGeometryCollection* RestCollectionIn)
{
SetRestCollection(RestCollectionIn);
}