Gratis Sent Me the Wrong False Nails and I Cannot Use the Product I Ordered

I placed an order through Gratis online and picked it up from the store, but one of the three false nails I ordered turned out to be completely different from what I selected and is a model I cannot use. I am now requesting an exchange but have no idea how the process works, and honestly, I am not keen on dealing with the hassle this has caused. The store was busy when I picked up my order, so I only checked the item count without examining the specifics. The product I received has nothing to do with the one I ordered. The first is what they sent me, and the second is what I actually added to my cart. I would appreciate prompt assistance in resolving this issue.