To customize the QueryViewer control you need to associate a class to it (Appearence section).
Then, open the associated Web Theme object and locate the QueryViewer node matching the class you selected:
Depending on the control output Type (Table, Pivot Table, Chart or Card) property, you will find a section to set the desired UI properties:
This customization is available since GeneXus 15 upgrade 12.
HowTo customize Map visualization in QueryViewer control