Unlike files on disk, database tables don't have a generic "timestamp" which identifies when they last changed. Without a database/vendor specific custom solution, you must re-query the data to detect new data. (Microsoft Access is an exception, since it uses a single file on disk which Omniscope keeps track of.)

In DataManager, in the Database block, click the spanner/wrench icon "Block options" and choose "Update options". In the dialog, choose "Scheduled" and configure how often you want Omniscope to re-query the data. This will depend upon how immediately you want to detect changes, and how much strain you want to place on your database server and network.

Now in the main menus, choose "Data > Automatic refresh > Retrieve new data and apply ***". You have 3 variant behaviours, which refer to when data in DataManager is applied to your main Omniscope views.
"Notify" means you'll get a red button when new & changed data is detected.
"Apply when idle" means Omniscope views will be updated when you stop using Omniscope for several seconds.
"Apply immediately" means Omniscope views will be updated as soon as the changes are detected; this might interrupt your workflow.