Customization (and theme installation) is not included in item support at Themeforest (and Codecanyon).
Please read the following page;
What is customization?
For example; Adding a new color scheme to the theme/plugin, adding a slider from another theme, changing layout, adding a plugin compability (like woocommerce), including a feature that is not included in the theme/plugin etc.
We don’t provide customization services. If you need professional help with installation WordPress, setting up a WordPress theme, implementing a new feature or customizing a theme or a plugin, you can buy a service from Envato Studio with a small fee.