Modify current summary report

How to add additional column in the current summary report

Can we get more detail on which summary "report" and how you created it, and where you're looking in the TDP GUI?

That said, let's start here... if you're using the Visual Query Builder, then simply right-click in the diagram whitespace and choose Calculated Column, as shown below. There's also the ability to send a copy of your data to the Transform & Cleanse engine (in Professional versions of TDP) to create additional columns there.