Doadmin permissions for spatial_ref_sys in postgis

I’ve created a Managed PostgreSQL Database with the Postgis extension. It creates the spatial_ref_sys table with the list of supported reference projections for spatial queries. I need to add a new projection to spatial_ref_sys but it gives the error: permission denied for table spatial_ref_sys. I’ve used the doadmin user to create the extension and the table spatial_ref_sys is owned by postgres user. I can’t change the ownership, neither the permissions. How can I do that with my user privileges?

Thanks