If you intend to automatise the import of calling lists, you will need to build an application that gets the lists from whatever source, manipulates them and then populates the OC database with insert queries.
An alternative would be using a HTTP request to OCS of an AddRecord type - see the Outbound Reference guide.
Lastly, I’m fairly confident that at least in the past the Interaction SDK was exposing a way to add records, you may want to check the relevant docs.
There is no magic way, as said, SQL INSERT queries would do the job, just create a JOB, a Trigger or something on your other DBM. If you have no clue ask a DBA.
On Genesys side as Fra said would be via APIs but I think will be too much work just for a pure INSERT.
Job on your BD Server (MSSQL, Oracle, etc). You program to start at 11pm for example, read your tables and do an insert on OCS calling lists, aka, tables