We would suggest that you add an image and link it to an external URL. Kindly see the screenshot below. Please note that that call to action button "Pre-Order Now" is actually an image that you can edit and link to an external URL. After adding an image, you can hover around it and click "Edit" to access more options.
You can also opt to open the external URL in a new window as not to lose the current one.
Trust this helps.