I'm Ann, from the team here at Shopify :)
It sounds like what you're looking for is one of the quantity break apps we have in our App Store. In this case, these apps will give a discount based on quantity in a cart, and you can specify that it only applies to one product, so, for example, buy two or more sneakers and get a discount, or you can apply it to all products in a store, so buy two or more items and get a discount. The options for how you set these up are up to you! Here is a list of a few of these apps for you to check out:
All these apps come with free trials, so you can take a look and see which option will be best for you and your store. It's also good to note that these apps were created by third party companies. This means, that if you had any questions about them, how to install them in your store, or anything like that, your best bet will be to reach out to the developers who created the apps directly. Their contact information can be found on the app store's page.
I hope this helps! If you have any more questions or concerns feel free to reach out to us on this thread :)
Have a great one,