Drupal 8 Metatag and Media Entity modules to set meta image tags
If I understand your question correctly you'll need to do the following:

Check on your modules page that the &quot;Metatag: Open Graph&quot; submodule
is enabled.
Go to metatag config page (Configuration &gt; Search and
metadata &gt; Metatag).
Add a new &quot;default metatag&quot; and select your
content type in the &quot;Type&quot; selectbox.
Fill in the rest of the fields similar like following picture (just don't forget to use your own field names:


Here are some things you need to know about my tokens:

field_teaser_img: is the fieldname of my media entityreference on my
content type.
field_me_img: is the fieldname of my image field
on my media entity type.
facebook: is the imagestyle name I
created for these metatags
height, mimetype &amp; width: are
property fields of the media entity type yet I didn't create those
fields but it does seem to work.

I hope this helps.