MM, it need not be returnt to the store. It states on their site,
"For any age-restricted products that can't be delivered because the customer is underage or doesn't have ID, please dispose of these responsibly. You don’t need to return them to the restaurant or store, but you should not:
give them to anyone under the age of 18
dispose of them somewhere they are likely to be accessible to anyone under the age of 18
sell them on to anyone else
give them to anyone who is already drunk
If you can’t deliver part of the order because the customer doesn’t have ID, is too young, or is already drunk you'll still be paid the full fee for the order, and we’ll contact the customer directly."