For unreleased result sets:


1. Go to 'Release Results' and select the result set you want to set to default.


2. Double click on the result, right-click on the table and select 'Change to Default Instance'. 


For released result sets:


1. Go to 'Management Overview' and search for the Room.


2. Select the result set you want to change to default by double-clicking on it.


3. Right-click on the table and select  'Change to Default Instance'.