Unfortunately, we cannot connect products with add-ons. We can advise solving this issue 2 ways:
If your add-ons are not selling well, you might consider simply removing them.
If you wish to keep your add-ons, please create a new tour option for the same tour with the pricing already including value of the add-on. Then, delete the add-on from the original option. Please create a new, corresponding option in your inventory management system and map it to the correct tour option on GetYourGuide.