After not being able to install the software (leap 15.0), to create an instance
(leap 15.1), I now succeeded on 15.2 to install and create an 389ds LDAP
instance with yast (localhost).
But this does not help me: even the "Directory Manager" does not have the
permissions to add a new domain just below the basedn (dc=groland,dc=de). 

ldap_add: insufficient access (50)
        additional info: Insufficient 'add' privilege to add the entry
'dc=prometeus,dc=groland,dc=de'

The command has been (as root)
ldapadd -x -f <filename>
Which step is missing after creating the instance?

It is problematic that all the 389ds standard documentation does not work as no
console, no cockpit etc. is available on leap. Additionally I do not find any
opensuse specific documentation how to proceed (no for leap 15, 15.1 either).

Schema included: 00core, 05rfc4534, 06inetorgperson, 10rfc2307, and 99user.
The data have been extracted from a slapcat dump out of the running openldap
instance.
Thanks for your help!