It may vary depending upon the browser or the app version you would be viewing the desired setting from, but judging by the above linked support article you should be able to add the owner if they aren't already on airbnb--or in the sense that they need to add you as their co-host for a particular listing when they have already created it.
In this case, it seems you have created it instead--I don't see why it shouldn't work both ways.
If you still experience issues, try reaching out to techincal support to troubleshoot, since I really do feel it would be a matter of outdated app versions/needing to update your browser/maybe switching to a different browser to verify the feature's existence or not/etc.