Open this PHP file:
/templates/YOUR_TEMPLATE/html/productdetails/default.php
and look for this line:
<!-- FACEBOOK LIKE Button (HTML5) BEGIN -->
<div class="fb-like" data-href="https://www.facebook.com/flexibleWD" data-send="false" data-width="220" data-show-faces="false" data-colorscheme="light"></div>
<!-- FACEBOOK LIKE Button (HTML5) END -->
and replace it with the one you generated through dev.facebook.com. Use the HTML5 version.
TIPS: don't do anything with the JavaScript SKD, it has already been added to CoolMart.
Regards,
Support.