if your notification is using event to trigger then please create a custom action same as given below and use it in the flow to trigger your notification.
gs.eventQueue("event_name","GlideRecordObject",Param1, parm2);
Param1 & 2 are optional parameters. Hence if required you can use it or ignore.
then only the way to trigger your notification is to make changes to the table records on which you created the notification, that meets the condition you define in your notification.
For example the below email notification to get trigger then we need to have the logic in flow to make additional comments to incident record which meets the condition defined in the email notification.
