Deep facate - reindexing

Hi everyone :wave:,
Can anyone give me a hand on placing the touch for reindexing or what the by_external_service_changed? should have in the body?

That’s my attribute that creates a facate for delivery and booking:

attribute :by_external_service do
  external_services.select { |es| es.categories.include?('delivery') || es.categories.include?('booking') }.map do |es|
  { category: es.external_categories.pluck(:name)
  end
end

def by_external_service_changed?
  false
end

And the touch is placed in ExtrnalServiceLink

class Business < ApplicationRecord
  has_many :external_services, through: :external_service_links
end

class ExternalServiceLink < ApplicationRecord
  belongs_to :business, touch: true
  belongs_to :external_service
end

class ExternalService < ApplicationRecord
  has_many :external_service_links, dependent: :destroy
  has_many :external_categories, as: :categorisable, inverse_of: :categorisable, dependent: :destroy
end

class ExternalCategory < ApplicationRecord
  CATEGORIES_TYPES = { external_service: %w[ delivery booking ...] }.freeze

  belongs_to :categorisable, polymorphic: true
end