The non-owner member in a group with update capabilities is unable to modify the layer schema in the item details.

Solución alternativa

1. Add the layer to a new map with full editing capability in Map Viewer.
2. Expand the layer, and open the attribute table.
3. There is an option to add a field under Table Options. Add or delete a field in the hosted feature service in the ArcGIS REST API URL.

Pasos para reproducir