public Task ActivateAsync()

{
  await QueuedTask.Run(() =>
  {
    // Get all templates for the layer
    var templates = featureLayer.GetTemplates();
    if (templates.Count == 0)
      return;
    // Get the first template - alternatively get a specific template
    var template = templates.First();

    // Activate the template without changing the current tool
    template.ActivateAsync();
  });
}