Custom Widget Button
The default widget button appears on your product page when an out of stock product is selected.
You can easily replace this button with your own.
Create an image for your button in PNG, GIF or JPEG format. The dimensions of the image can be whatever you like - Back in Stock will detect it automatically.
Upload your custom button to your store theme using the template editor. You can then visit widget settings and choose your image from the Button image dropdown.
Inline product page button
It’s also possible to have the widget button sit in the product page by adding some HTML to your product template.
See Developers: Product page button for more information.