You need to do the following:
public:
UPROPERTY(EditAnywhere, BlueprintReadWrite, Category = "Widgets") TSubclassOf<class UUserWidget> HealthWidgetTemplate;
private:
UPROPERTY() UHealthWidget* HealthWidget;
Then in your code you can create it:
if(HealthWidgetTemplate){
HealthWidget = CreateWidget<UHealthWidget>(this, HealthWidgetTemplate, FName("MyName"));
}