?
Select all chords on the chord track, use the drop-down menu in the info line to change the “Root Key” selected chords are transposed
Note: Root Key is the wrong term for this, it should simply be ‘Root’.
Edit: Wow. I saw several weird behaviors that I could not consistently reproduce. I had to clear the selection (Select None) in order to repeat the function dependably.
Man, you have to really love Cubase to learn and tolerate all the special workarounds and quirks.