How to set game window to be topmost at Runtime?

I have searched many document and API. In GameEngine.cpp i found that windows can be set top most when construct. But how to set this at Runtime? All idea i can find is that return whether is top most window.
Thanks.

	TSharedRef<SWindow> Window = SNew(SWindow)
	.Type(EWindowType::GameWindow)
	.Style(bUseBorderlessWindow ? &BorderlessStyle : &FCoreStyle::Get().GetWidgetStyle<FWindowStyle>("Window"))
	.ClientSize(FVector2D(ResX, ResY))
	.Title(WindowTitle)
	.AutoCenter(AutoCenterType)
	.ScreenPosition(FVector2D(WinX, WinY))
	.MaxWidth(MaxWindowWidth)
	.MaxHeight(MaxWindowHeight)
	.FocusWhenFirstShown(true)
	.SaneWindowPlacement(AutoCenterType == EAutoCenter::None)
	.UseOSWindowBorder(!bUseBorderlessWindow)
	.CreateTitleBar(!bUseBorderlessWindow)
	.ShouldPreserveAspectRatio(bShouldPreserveAspectRatio)
	.LayoutBorder(bUseBorderlessWindow ? FMargin(0) : FMargin(5, 5, 5, 5))
	.SizingRule(bAllowWindowResize ? ESizingRule::UserSized : ESizingRule::FixedSize)
	.HasCloseButton(bAllowClose)
	.SupportsMinimize(bAllowMinimize)
	.SupportsMaximize(bAllowMaximize)
	.IsTopmostWindow(true);

API:SWindow | Unreal Engine Documentation