We need to create classes ChainingBackend(DSLdapObject) and ChainingBackends(DSLdapObjects). We need to bring the chaining backend specifics to it.
The information about how the objects should look like can be found in Admin guide:
https://access.redhat.com/documentation/en-us/red_hat_directory_server/10/html-single/administration_guide/index#Configuring_Directory_Databases-Creating_and_Maintaining_Database_Links

We can use existing classes as examples.
https://pagure.io/lib389/blob/master/f/lib389/backend.py#_388
https://pagure.io/lib389/blob/master/f/lib389/backend.py#_560

We can copy some code from there. Though we need to make some modifications (for example, self._basedn = DN_LDBM -> self._basedn = DN_CHAIN, etc.) Some methods should be changed too.