Add selected to relationship

[KristinaMartinelle1]

In a WebApp is there a way to easily add selected features to a relationship like we do in ArcGIS Pro? What I have been able to do is create a new post in the related table but not found any way to relate to an existing post in the related table.

Relationship classes for this point

The plus sign gives me an opportunity to create a new post in the related table. But how do I create a relationship to an existing row?

Hope there is a possibility that I missed!

Best regards

Kicki Martinelle