First I would verify this is the correct query you are looking for. This should be the correct query, but check Object Designer to be sure.
Object Designer --> Incident Management --> Incident --> Query - Default Query
This field should be the query you are currently using when you click add child incident.
What I would do is copy the Default query and modify the copy how ever you like. Then go back to Object Designer and change it to the new query. Of course name it something different so that it is easily identifiable. Upon selecting the query in Object Designer, it should set it for the action.
I have modified ours to use a prompt user for the incident number/ref number. this allows us to find the exact one immediately, as opposed to flipping through a lot of pages.
Hope this helps,
Actually, my default query in objectDesigner - Incident Management - Incident is called "All Incidents" and it's different from the "default incident query" which prompt when I click on "add child incident" in my problem process.