Access selected column from Model1 to Model2

I have 2 tables. Table 1 and table 2/table 1 model and table 2 model. One of my columns in table 1 is : order, in my table 2, i want to call the order column in my table 1 to set a default value before it saves.

Question: How can I get the order column from table 2?

table 2/table 2 model

class Itinerary < ApplicationRecord
  belongs_to :user, foreign_key: :created_by
  belongs_to :activity
  before_save :default_value, :count_all_activity
  after_save
  # has_many :activity_itineraries, foreign_key: :created_by
  has_many :activity_itineraries, inverse_of: :itinerary
  has_many :activities, through: :activity_itineraries

  validates :user, presence: true
  validates :title, presence: true, length: { maximum: 20 }
  validates :no_of_days, presence: true,
               :numericality => true

  private

  def default_value
    self.order = "1"
  end

  def count_all_activity

  end
end