Renouncing Ownership of Seventh Year Fruits

Honorable Rabbis, shalom! We purchased discounted products at two separate sales: grape juice ‘otzar beis din’ (whereby the buyer only pays for the work involved in harvesting/packaging/marketing the product, but not the product itself) and wine from a non-Jewish harvest. (Both were actually bought by mistake, had I known when I prepaid for the products, I wouldn't have bought them.) Now, the question is what to do. Do I need to ‘destroy’ the products by renouncing ownership, and if so, do I need to renounce my ownership in front of three people? And do these three need to be eligible to testify (not relatives)? And can I renounce the ownership in my building's stairwell by also renouncing ownership of a square cubit in which I placed the bottles (since I also have a share in the building's common areas)? Thank you very much and happy holiday!

Shalom and happy holiday!
You can return them to the store.
You can keep them with you and renounce your ownership immediately.
You should place them in an unguarded place, and renounce ownership in front of any three people, even if they are related to each other. But do not renounce them in front of your household members whom you support.
In a stairwell where other people pass by, you can renounce them, even without renouncing your part in the building.