Hi,
You can do this by following below steps.
1. Add a button and go to button properties.
2. Click on ‘Rules’ button.
3. In Rules window click on ‘Add’ button.
4. In Rule window click on ‘Add action’ button.
5. In action drop down select set a field’s value.
6. Select a query field for ‘field’ text box and leave the value text box as blank.
7. Click ‘OK’ until all windows get closed.
8. Repeat the steps 4, 5 and 6 for all query fields.