Free gifts are always tied to the purchase of a specific product. If you keep the associated product, you are also entitled to keep the free gift accordingly. However, if you return the item, the free gift must also be returned.
Exceptions to this rule:
Exempt from this rule are, of course, free samples and free gifts marked as "Try Me" on the invoice. You can keep these in any case.
You can find all the information on how to return an item in our article:
How can I return an item?