Hello,

1/ Login into your ThemeForest account, download child theme, install and activate it. All your parent theme settings would remain the same.

2/ Go to Appearance > Editor http://prntscr.com/jcagzo add the snippet to functions.php file

3/ Find the place on the screen provided above and insert there ID of the product.

In order to see the product ID enter its editing mode and you will see in url.

Best Regards