Thank you for the very quick answer! I don't want to display the link on front end, but on the edit post / user relationship metabox.
Maybe I didn't understood your answer, I am not a dev, sorry. And I would understood if this this question is beyond the scope of your support.
The plugin MB Relationships has not supported to link to the post selected on the backend yet. I'm going to create a feature request for the developer team to support this case.
OK. I guess is the same for my other post related to metabox relationship custom fields.
FYI pods relationship feature adds a simple edit link near to the related items once selected. A similar solution would be nice.