In order to set up base configurations for Magento 2 Open Graph Module please go to Stores > Configuration  Magefan Extensions > Open Graph.

General

1. Enable an extension choosing correspondingly Yes in Enable Extention select box.

2. In a Default OG Image, you can set Open Graph image by default. The chosen image will be used for a page if it is not redefined, for example in product settings.

3. The Open Graph description can be set  by default in a Default OG Description.

Magento 2 OG Extention,General

Once you have finished with all of the configurations don't forget to press the Save Config button.

Magento 2 OG  Configurations