how can i add tier discount script in shopify debut theme without using script editor app

I’m new to Shopify. please anyone can answer. just how to add a discount script in debut default theme without using any script editor app.
this is a script for spend X amount and get a Y% discount… I got this ruby script in Shopify.

  PRODUCT_DISCOUNT_TIERS = [
    {
   product_selector_match_type: :include,
   product_selector_type: :tag,
     product_selectors: ["your_tag"],
     tiers: [
       {
      quantity: 2,
    discount_type: :percent,
    discount_amount: 10,
    discount_message: '10% off for 2+',
  },
  {
    quantity: 5,
    discount_type: :percent,
    discount_amount: 15,
    discount_message: '15% off for 5+',
  },
],
  },
 ]
   class ProductSelector
    def initialize(match_type, selector_type, selectors)
    @match_type = match_type
    @comparator = match_type == :include ? 'any?' : 'none?'
    @selector_type = selector_type
    @selectors = selectors
   end

   def match?(line_item)
    if self.respond_to?(@selector_type)
      self.send(@selector_type, line_item)
    else
  raise RuntimeError.new('Invalid product selector type')
  end
end

  def tag(line_item)
   product_tags = line_item.variant.product.tags.map { |tag| tag.downcase.strip }
   @selectors = @selectors.map { |selector| selector.downcase.strip }
   (@selectors & product_tags).send(@comparator)
  end

   def type(line_item)
   @selectors = @selectors.map { |selector| selector.downcase.strip }
   (@match_type == :include) == @selectors.include? 
   (line_item.variant.product.product_type.downcase.strip)
  end

  def vendor(line_item)
@selectors = @selectors.map { |selector| selector.downcase.strip }
(@match_type == :include) == @selectors.include? 
 (line_item.variant.product.vendor.downcase.strip)
 end

 def product_id(line_item)
(@match_type == :include) == @selectors.include?(line_item.variant.product.id)
 end

 def variant_id(line_item)
(@match_type == :include) == @selectors.include?(line_item.variant.id)
 end

 def all(line_item)
  true
 end
  end
  class TieredPricingCampaign
    def initialize(campaigns)
    @campaigns = campaigns
   end

  def run(cart)
   @campaigns.each do |campaign|
  product_selector = ProductSelector.new(
    campaign[:product_selector_match_type],
    campaign[:product_selector_type],
    campaign[:product_selectors],
  )

  applicable_items = cart.line_items.select { |line_item| product_selector.match?(line_item) 
 }

  next if applicable_items.nil?

  total_applicable_quantity = applicable_items.map(&:quantity).reduce(0, :+)
  tiers = campaign[:tiers].sort_by { |tier| tier[:quantity] }.reverse
  applicable_tier = tiers.find { |tier| tier[:quantity] <= total_applicable_quantity }

  next if applicable_tier.nil?

  discount_applicator = DiscountApplicator.new(
    applicable_tier[:discount_type],
    applicable_tier[:discount_amount],
    applicable_tier[:discount_message]
  )

  applicable_items.each do |line_item|
    discount_applicator.apply(line_item)
  end
end
end
end

  CAMPAIGNS = [
  TieredPricingCampaign.new(PRODUCT_DISCOUNT_TIERS),
  ]

CAMPAIGNS.each do |campaign|
campaign.run(Input.cart)
end

Output.cart = Input.cart

Is it possible to add the script without using script editor and Shopify plus app. please anyone helps me.