It is interesting how it is just implied that you would know HOW to switch the settings from File to DB or back. But not mentioned. Took me a bit of searching but found it, so will add it here to help the next guy who finds this.
The line in ism-config would be:
Default (and absent) is =file
This is where the MigrateSettings tool is useful to copy the File settings into the DB. And then there is a warning that:
If you modify the client settings mode, you must also set the com.netiq.idm.rbpm.updateConfig-On-StartUp property to true in the ism-configuration.properties file. By default, the property is set to false. Setting this property to true ensures that the application configurations are correctly refreshed and updated in the database after Tomcat is restarted.
Conviently, the docs for MigrateSettings is the next page: