In order to configure OG Tags for Magento 2 CMS Page please go to Admin Panel > Content > Pages.

Magento 2 OG Tags, CMS Page

Then choose a page you are interested in and press the select button in order to start editing it.

Magento 2 OG Tags,CMS Page

Find the Open Graph Metadata section.

Open Graph Metadata

1. Set an Open Graph title in OG Title field. In case you haven't set it up the Meta Title will be used. If it isn't configured either Page Title will be used.

2. In the OG Description set the Open Graph description of the page. Meta description of the page will be used in case an OG description hasn't been set up.  the Default Description will be used, if there are none of the descriptions configured.

3. In the OG Image set the Page Open Graph image (Facebook Image). If you haven't set it up the Default OG Image will be used.

Magento 2 OG Tags CMS Page,Open Graph Metadata

Once you have finished don't forget to press the Save button.

Magento 2 OG CMS Page,Save