To enable the configuration settings,
- Go to the Magento 2 Admin Panel.
- On the left navigation bar, click on Stores and then on Configuration.
- On clicking it you will be navigated to the Configuration page.
In the left panel click on Custom to Configurable. The sections open as shown below:
- Under the settings in Enable option select Yes to start with the converting of the products.
As soon as you enable it, the products will be imported into the catalog.
- Click on the Save Config button to save the settings.