default-acf-flexible-content.php

add_filter( 'acf/load_value/name=content_blocks', 'default_fields', 10, 3 );
function default_fields( $value, $post_id, $field ) {

  // Only add default content for new posts
  if ( $value !== null ) {
    return $value;
  }

  // Only add default content for certain post types
  if ( ! in_array(
		get_post_type( $post_id ),
		array(
			@TODO Post Types
		) ) ) {
		return $value;
	}

  // Set up your initial post, then get the field id's of the settings you want to set
  // They look like: field_5b4e57efd0660_field_5b4e63e479d81
  // Add them after the acf_fc_layout
  $value = array(
    array(
      'acf_fc_layout' => 'name_of_layout',
    ),
    array(
      'acf_fc_layout' => 'another_layout',
    )
  );

  return $value;
}