+ plugin Article logo errors

With Article I get logo errors in structured data test tool
https://search.google.com/structured-data/testing-tool#url=https%3A%2F%2Fwww.cherwell.com%2Fblog%2Fitsm-news-roundup-change-management

Error
A value for the logo field is required.
The property logo is not recognized by Google for an object of type Article.

And this warning:
mainEntityOfPage
The mainEntityOfPage field is recommended. Please provide a value if available.

How can I fix this?
Thanks