First, click on the "Create customization" button and choose between Simple or Advanced customization.

On the next screen, you'll notice at the bottom of the page a window where you can enter any shipping method present on your checkout page, and once you've entered the method, simply click "Add shipping method" and the new method will be added.

Now you can manage the new shipping method as you prefer.

NB: We recommend handwriting the new shipping method to avoid copying errors from shortcuts such as invisible spaces or special symbols.