Fetchin relationship data

I have

Product model

  has_many :licence_products, dependent: 
 :nullify
 has_many :licences, through: :licence_products

Licence model

has_many :licence_products, autosave: true, 
dependent: :destroy
has_many :products, through: :licence_products

LicenceProduct model

  belongs_to :licence
  belongs_to :product

NOw when I delete a product, I want to update the product_id of licence_products table to nill, where (licence_status = draft)

status is in licence tables, product_id is in licence_products table

Product where @draft_licence= product.licences.status == draft , update @draft_licence.licence_products.product_id = nill.

I am not able to update the query . How can I do this?

    authorize @product
if(@product.licences.present?)
 @licences_draft = @product.licences.where(:aasm => "Draft").all
if(@licences_draft.exists?)
  @licences_draft.licence_products.update_all(:product_id => nil)
end