Hey, not sure if it’s still relevant but i’m using next code 
/** Assgin bind funtion to the health bar */
UProgressBar* HealthBarWidget = (UProgressBar*)GetWidgetFromName(TEXT("HealthIndicator"));
if (HealthBarWidget != nullptr)
{
HealthBarWidget->PercentDelegate.BindUFunction(this, "GetHealthPercentage");
HealthBarWidget->SynchronizeProperties();
}