Bought custom navigation menu from codecanyon, how to change feature.php?

For what I understand you want to implement a custom menu in your wordpress theme.

First of all you have to understand the template structure of the theme you’re using. Most themes have the navigation menu in the header.php or templates/head.php, it depends.

Additionally, will you use a static menu or dynamic? Dynamic meaning you’re adding the pages (created via wordpress dashboard) automatically in the navigation menu structure. Static is just a copy paste operation of the nav-menu.

Lastly, the author of the nav-menu you’ve purchased is using wordpress as well. It may be worth asking him for advice.

Hope it helps you moving forward.