correction.rb

corrected = []

File.open('original.txt', 'r').each_line do |date|
 new_date = Time.parse(date, '%Y-%m-%d %H%M%S')
 
 if new_date.month == 6 && new_date.year == 2021
   corrected << new_date.next_month.beginning_of_month
   next
 end
 
 while new_date.past?
   next_date += 3.months
 end
 corrected << new_date
end

File.open('corrected.txt', 'w') do |f|
 corrected.each { |date| f.puts date }
end

script.rb

subs = SolidusSubscriptions::Subscription.joins(:tags).where(tags: { name: 'legacy'}).distinct

subs.each do |sub|
  new_date = sub.actionable_date

   if new_date.month == 6 && new_date.year == 2021
     sub.actionable_date = new_date.next_month.beginning_of_month
     sub.save!
     next
   end

   while new_date.past?
     new_date += 3.months
   end
   sub.actionable_date = new_date
   sub.save!
 end
end

ah!!! I meant notes!

SolidusSubscriptions::Subscription.where.not(notes: nil).

The imported subscriptions will have the id in the notes field.