How to setup pre-order products?

How to change Pre - Order button to Add to cart button on product page. Instead of Add to cart button it is showing Pre-Order button, why is that?

Pre-order products are products that will continue to be sold when they are out of stock. With pre-order products, they will be still visible on store and the button "Add to cart" of these products will be change to "Pre-order" instead of a "Sold out" button.

To setup a pre-order products, please follow these steps:

1. From your admin, go to Products

2. Click to the product you want to edit

3. Scroll down to Inventory section, tick to "Continue selling when out of stock" checkbox